Report of Independent Registered Public Accounting Firm

To the Participants and Administrator of the Genzyme Corporation 401(k) Plan:

In our opinion, the accompanying statements of net assets available for benefits and the related statement of changes in net assets available for benefits present fairly, in all material respects, the net assets available for benefits of the Genzyme Corporation 401(k) Plan (the “Plan”) at December 31, 2006 and 2005, and the changes in net assets available for benefits for the year ended December 31, 2006 in conformity with accounting principles generally accepted in the United States of America. These financial statements are the responsibility of the Plan’s management. Our responsibility is to express an opinion on these financial statements based on our audits. We conducted our audits of these statements in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, assessing the accounting principles used and significant estimates made by management, and evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

Our audits were conducted for the purpose of forming an opinion on the basic financial statements taken as a whole. The supplemental schedule of assets (held at end of year) is presented for the purpose of additional analysis and is not a required part of the basic financial statements but is supplementary information required by the Department of Labor’s Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. This supplemental schedule is the responsibility of the Plan’s management. This supplemental schedule has been subjected to the auditing procedures applied in the audits of the basic financial statements and, in our opinion, is fairly stated in all material respects in relation to the basic financial statements taken as a whole.

As discussed in Note 2, effective for plan years ended after December 15, 2006, FASB Staff Position Nos. AAG INV-1 and SOP 94-4-1, “Reporting of Fully Benefit-Responsive Investment Contracts Held by Certain Investment Companies Subject to the AICPA Investment Company Guide and Defined-Contribution Health and Welfare Pension Plans,” was required to be implemented. Therefore the presentation of the 2006 and 2005 financial statement amounts include the presentation of fair value with an adjustment to contract value for such investments.

/s/ PricewaterhouseCoopers LLP

Boston, Massachusetts

June 29, 2007

Genzyme Corporation 401(k) Plan

Statements of Net Assets Available for Benefits

As of December 31, 2006 and 2005

	2006		2005
Assets
Investments, at fair value:
Registered investment companies, pooled separate accounts and guaranteed accounts	$	364,516,041	$	280,311,840
Genzyme Corporation Common Stock	41,852,792		45,952,576
Participant loans	5,122,880		4,221,598
Total investments	411,491,713		330,486,014
Receivables:
Employee contributions	—		1,926
Employer contributions	1,645,918		1,197,185
Total receivables	1,645,918		1,199,111
Net assets available for benefits at fair value	413,137,631		331,685,125
Adjustment from fair value to contract value for fully benefit-responsive investment contracts	1,119,188		621,794

Net assets available for benefits	$	414,256,819	$	332,306,919

The accompanying notes are an integral part of these financial statements.

Genzyme Corporation 401(k) Plan

Statement of Changes in Net Assets Available for Benefits

For the Year Ended December 31, 2006

	2006
Additions to net assets attributed to:
Investment income:
Interest and dividend income	$	4,035,215
Net appreciation in fair value of investments	31,367,958
Total investment income	35,403,173
Contributions:
Employee	41,484,178
Employer	22,103,044
Rollovers	3,953,122
Total contributions	67,540,344
Total additions	102,943,517

Deductions from net assets attributed to:
Benefit payments and withdrawals	(20,902,615		)
Participant expenses	(91,002		)
Total deductions	(20,993,617		)
Increase in net assets available for benefits	81,949,900
Net assets available for benefits:
Beginning of year	332,306,919
End of year	$	414,256,819

The accompanying notes are an integral part of these financial statements.

Genzyme Corporation 401(k) Plan
Notes to Financial Statements

1. Plan Description

The following description of the Genzyme Corporation 401(k) Plan (the “Plan”) provides only general information. Participants should refer to the Summary Plan Description and Plan documents for a more complete description of the Plan’s provisions.

General

The Plan, a defined contribution plan pursuant to the authorization of Genzyme Corporation’s (“Genzyme”) Board of Directors (the “Genzyme Board”), was established effective January 1, 1988 to provide a long-range program of systematic savings for eligible employees (the “Participants”). The Plan was established and operates under the provisions of Section 401(a) of the Internal Revenue Code of 1986, as amended (the “Code”), and includes a qualified cash or deferred arrangement, as described in Section 401(k) of the Code, for the benefit of eligible employees of Genzyme. The Plan is subject to the provisions of ERISA. Employees of Genzyme and Genzyme’s wholly-owned subsidiaries in the United States of America are eligible to participate in the Plan if they are at least 21 years of age, and are scheduled to complete annually (or have completed within an applicable measuring year) 1,000 hours of service.

Plan Administration

The Plan is administered by the Genzyme Benefit Plans Committee (the “Committee”), the Plan Administrator as defined by ERISA. The Committee was established effective October 4, 2001 to replace its predecessor, the Genzyme 401(k) Committee. The Committee consists of at least three persons who are appointed by the Genzyme Board. The Committee has the authority to determine the eligibility of employees, interpret the Plan provisions and make final decisions in disputes involving the rights of any Participant’s interest in the Plan. The Committee, as the named ERISA fiduciary, also has the responsibility of selecting and monitoring the investment funds under the Plan.

The Genzyme Board retains the powers to amend or terminate the Plan and to perform all functions of a plan sponsor. The Compensation Committee of the Genzyme Board is authorized to perform any acts permitted or required to be performed by the Genzyme Board under the terms of the Plan. The Compensation Committee has delegated to the Committee its authority to adopt certain amendments to the Plan.

Prudential Retirement Insurance and Annuity Company (“Prudential”) is the trustee, custodian and record keeper of the Plan.

Plan Amendments

The Committee amended the Plan on March 1, 2006, effective as of October 1, 2005, to amend Articles I and IV to clarify the authority of the Committee and on December 27, 2006 primarily to:

· amend Article I to allow employees of Genzyme Therapeutic Products Limited to participate in the Plan effective January 1, 2007;

· amend Article VI, effective January 1, 2006, to implement the required limitations of elective contributions (which shall not include catch-up contributions or deferrals), non-elective contributions and employer matching contributions, by reason of an eligible employee’s qualified military service; and

· amend Article X, effective January 1, 2006, to further clarify certain circumstances when a Participant may make a hardship withdrawal of their pre-tax contributions and the earnings credited to those contributions and to allow the Participant to provide written representation that their immediate and heavy financial need could not be satisfied in whole or in part from other sources reasonably available to the Participant.

Participants should refer to the Summary Plan Description for a more complete description of these amendments.

Investment Options

The following participant-directed investment options were available to Participants during 2006:

· Prudential Separate Accounts:

· The Dryden S&P 500 Index Fund;

· The Templeton Foreign Account(1);

· The Small Cap Value/Perkins Wolf McDonnell Fund(1);

· The Small Cap Growth/Times Square Fund;

· The Lazard International Equity Account(1);

· The Core Bond/BSAM Fund (managed by Bear Stearns Asset Management)(1);

· The Large Cap Value Fund (sub-advised by Wellington Management)(1);

· The Large Cap Value Fund/LSV Asset Management Fund (sub-advised by LSV Asset Management)(2);

· The Mid Cap Value Fund (sub-advised by Wellington Management)(1);

· The Mid Cap Growth/Artisan Partners Fund(1); and

· The Mid Cap Value Fund/CRM Fund (sub-advised by Cramer, Rosenthal and McGlynn)(2).

· Guaranteed Accounts:

· The Guaranteed Income Fund (“GIF”); and

· The Guaranteed Securities Separate Account (“GSSA”)(1).

· The PIMCO Total Return Admin Fund(2);

· The Fidelity Puritan Fund;

· The Emerald Growth Fund(1);

· Wells Fargo Advantage Small Cap Value Z Fund(2);

· Thornburg International Value I Fund(2);

· The Heritage Mid Cap Stock Fund;

· The Growth Fund of America; and

· Genzyme Corporation Common Stock(3).

Reallocation of account balances among participant-directed investment options can be requested and processed on a daily basis.

(1) Effective March 1, 2006, these funds were eliminated from the Plan. Any amounts that remained in these funds as of that date were reallocated, at the direction of each Participant, to other funds in the Plan.

(2) Effective March 1, 2006, these Participant-directed investment options were added to the Plan.

(3) Contributions directed by Participants for investment in Genzyme Corporation Common Stock may be invested in short-term investments until the purchase of the shares of stock can be completed.

Employee Contributions

The Plan is a defined contribution plan. Prior to January 1, 2007, eligible employees could elect, through salary reduction agreements, to have up to 18%, or a maximum of $15,000, (adjusted under such regulations as may be issued from time to time by the U.S. Secretary of the Treasury) of their eligible compensation (as defined by the Plan) contributed on a pre-tax basis to the Plan each year on their behalf. Participants who are age 50 or older by December 31, 2006 may make catch-up contributions to the Plan, subject to annual limits. For 2006, the catch-up limit was $5,000. After 2006, the catch-up limit of $5,000 will be subject to adjustment for cost of living increases (as determined by the U.S. Secretary of the Treasury). Catch-up contributions are not eligible for matching contributions. Changes in withholding percentages are permitted on a pay period to pay period basis. New employees with funds held under a previous employer’s qualified plan are permitted to invest such funds into the Plan. These investments are classified as “rollovers” on the accompanying statement of changes in net assets available for benefits. A Participant’s salary reduction contribution for a plan year may be further limited by the administration rules of the Code if the Participant is considered to be a highly compensated employee within the meaning of the Code.

Effective January 1, 2007, the Plan was amended to increase the percentage of eligible compensation that eligible employees may elect to have contributed to the Plan each year on their behalf from 18% to 60%, or a maximum of $15,500.

Employer Contributions

Genzyme, as the employer, makes bi-weekly matching contributions equal to 100% of the elective contributions made to the Plan by the Participant to the extent that such elective contributions do not exceed 4% of the Participant’s eligible compensation for such pay period, and 50% of the amount of elective contributions made to the Plan by the Participant to the extent such elective contributions exceed 4%, but do not exceed 6%, of the Participant’s eligible compensation for such pay period. Genzyme’s contributions were $22,103,044 for the year ended December 31, 2006.

Participants may invest their contributions in increments determined at their own discretion. Employer contributions from Genzyme are invested as directed by the Participants. If a Participant does not provide direction with respect to the investment of the Participant’s contributions, that Participant’s contributions will automatically be invested in the GIF.

Participant and Forfeited Accounts

An individual account is maintained for each of the Plan’s Participants to reflect the Participant’s share of the Plan’s investment income, the employer’s matching contributions from Genzyme and the Participant’s contributions. Investment income or loss is allocated based on the balances of the Participants’ individual accounts, based on the funds in which the accounts are invested. Forfeitures are used to reduce future employer matching contributions from Genzyme. Forfeited, nonvested matching accounts used to reduce employer contributions from Genzyme during the year ended December 31, 2006 were $335,936. At December 31, 2006, forfeited accounts totaled $314,010, all of which remain available to offset future employer contributions.

Vesting

Effective January 1, 2006, any Participant who was an employee on January 1, 2006 became fully vested in all of his accounts and any employee hired after January 1, 2006 who participated is fully vested. Participants who were no longer employees as of January 1, 2006 did not and will not become fully vested unless:

· the Participant is rehired (subject to certain restrictions);

· Genzyme or one of its subsidiaries terminates its participation in the Plan, or permanently discontinues its contributions to the Plan, and the Participant is employed by that employer (or in certain circumstances formerly employed by that employer); or

· the Plan is fully terminated.

Benefits and Withdrawals

Benefits are distributable from the Plan upon the Participant’s (1) retirement from employment on or after he has attained age 65, (2) termination of employment by reason of his disability (as determined by the United States Social Security Administration), (3) severance of employment, or (4) death. In addition, in-service withdrawals of elective contributions may be made by a Participant who incurs a hardship (as defined in the Plan), and a Participant may obtain an in-service withdrawal of all or a portion of any rollover contributions he has made to the Plan and, upon attaining age 59½, all or a portion of his vested accounts under the Plan. Distributions from the Plan are made in the form of a lump-sum payment. This lump-sum payment includes cash and, at the Participant’s election, may include some or all of the Participant’s holdings of Genzyme Corporation Common Stock.

Loans to Participants

Participants may obtain a loan from the Plan collateralized by one-half of the Participant’s vested interest in the Plan. No loan may exceed the lesser of one half of the vested interest of a Participant or $50,000, and each loan must be at least $1,000. Repayment of loans is made in equal installments through payroll deductions over a term generally not to exceed five years. However, if the Participant is obtaining the loan to purchase a principal residence, a longer repayment period may be allowed. The maximum repayment period for a loan used to purchase a principal residence is specified as 20 years, and is required to be repaid before the Participant’s normal retirement date. Loan transactions are treated as net interfund transfers to or from investment funds, and from or to the Participant loan fund, as applicable. All loans bear interest at the prime rate as posted in the monthly rates section of the Wall Street Journal, unless the Committee determines that a different rate is to be used for a loan or a class of loans. The interest rates on loans outstanding as of December 31, 2006 ranged between 4.0% and 9.0%. As repayments are made, both principle and interest are added back to the investment funds in which the Participant’s account is invested.

The Plan had Participant loans outstanding of $5,122,880 at December 31, 2006 and $4,221,598 at December 31, 2005. Outstanding Participant loans are classified as participant-directed investments on the accompanying statements of net assets available for benefits.

2. Summary of Significant Accounting Policies

Basis of Accounting

The financial statements of the Plan are prepared under accounting principles generally accepted in the United States of America using the accrual method of accounting.

Investment Valuation and Income Recognition

Units of participation in the Prudential separate accounts are valued at the net asset value of units as reported to the Plan by Prudential, and are generally based on the closing sale price of the underlying securities on the last business day of the plan year, which approximates fair value. The Fidelity Puritan Fund, The Heritage Mid Cap Stock Fund, The Growth Fund of America, The Wells Fargo Advantage Small Cap Z Fund, The PIMCO Total Return Admin Fund and the Thornburg International Value I Fund are stated at fair value based on each fund’s reported net asset value on the last business day of the plan year. Genzyme Corporation Common Stock is stated at fair value based on the quoted end of day closing price on the Nasdaq National Market on the last business day of the plan year. Participant loans are valued at cost plus accrued interest, which approximates market value.

As described in Financial Accounting Standards Board Staff Position AAG INV-1 and SOP 94-4-1, “Reporting of Fully Benefit-Responsive Investment Contracts Held by Certain Investment Companies Subject to the AICPA Investment Company Guide and Defined-Contribution Health and Welfare and Pension Plans,” collectively referred to as the FSP, investment contracts held by a defined-contribution plan are required to be reported at fair value. However, contract value is the relevant measurement attribute for that portion of the net assets available for benefits of a defined-contribution plan attributable to fully benefit-responsive investment contracts because contract value is the amount Participants would receive if they were to initiate permitted transactions under the terms of the Plan. As required by the FSP, the Statement of Net Assets Available for Benefits presents the fair value of the investment contracts as well as the adjustment of the fully benefit-responsive investment contracts from fair value to contract value. The Statement of Changes in Net Assets Available for Benefits is prepared on a contract basis.

The Plan has adopted the financial statement presentation and disclosure requirements effective December 31, 2006 and has retroactively restated the Statements of Net Assets for the periods presented due to the adoption of the FSP. The effect of adopting the FSP had no impact on net assets which have been historically presented at contract value.

Purchases and sales of securities are reflected on a trade-date basis. Gain or loss on sales of investments is based on average cost. The Plan presents the net appreciation or depreciation in the fair value of its investments in the statement of changes in net assets available for benefits, which consists of the realized gains or losses and the unrealized appreciation or depreciation on those investments.

Interest income is recorded, as earned, on an accrual basis. Dividend income is recorded on the ex-dividend date.

Contributions and Benefit Payments

Employee contributions and matching employer contributions are recorded in the period the payroll deductions are made. Benefits are recorded when paid.

Use of Estimates

The preparation of the Plan’s financial statements in conformity with accounting principles generally accepted in the United States of America requires the Plan administrator to make significant estimates and assumptions that affect the reported amounts of net assets available for benefits at the date of the financial statements, the changes in net assets available for benefits during the reporting period and, when applicable, disclosures of contingent assets and liabilities at the date of the financial statements. Actual results could differ materially from those estimates.

Risks and Uncertainties

The Plan provides for various investment options in any combination of stocks, pooled separate accounts, mutual funds, and other investment securities. Investment securities are exposed to various risks, such as interest rate, market and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities can occur in the near term and that such changes could materially affect participant account balances, the amounts reported in the statement of net assets available for benefits, and the amounts reported in the statement of changes in net assets available for benefits.

Recent Accounting Pronouncement

FAS 157, “Fair Value Measurements.” In September 2006, the FASB issued FAS 157, “Fair Value Measurements,” which provides enhanced guidance for using fair value to measure assets and liabilities. FAS 157 establishes a common definition of fair value, provides a framework for measuring fair value under accounting principles generally accepted in the United States and expands disclosure requirements regarding fair value measurements. FAS 157 is effective for the Plan as of January 1, 2008. The Committee is currently evaluating the impact, if any, the adoption of FAS 157 will have on the Plan’s financial statements.

3. Investment Contract with Insurance Company

Prior to March 1, 2006, the Plan participated in a contract with Prudential via investments in the GIF and the GSSA, both of which by definition are considered to be guaranteed investment contracts, or GICs. Effective March 1, 2006, the GSSA was eliminated from the Plan. Prudential commingles the assets of the GIF with other assets. In certain instances when total distributions or transfers in the GIF within a calendar year exceed pre-determined thresholds, transactions in the GIF may face certain restrictions, in accordance with the contract terms. This could potentially result in the GIF not being fully benefit-responsive in certain instances.

As described in Note 2, because the guaranteed investment contract is fully benefit-responsive, contract value is the relevant measurement attribute for that portion of the net assets available for benefits attributable to the guaranteed investment contract. Contract value, as reported to the Plan by Prudential, represents contributions made under the contract, plus earnings, less Participant withdrawals and administrative fees. Participants may ordinarily direct the withdrawal or transfer of all or a portion of their account balances at contract value.

As of December 31, 2005 and upon discontinuance of the contract effective March 1, 2006, the concept of value other than contract value did not apply to the GSSA. Therefore, as of December 31, 2005, the fair value amount of the GSSA was equal to the contract value for this account.

Interest is credited on contract balances using a single “portfolio rate” approach. Under this methodology, a single interest crediting rate is applied to all contributions made to the product regardless of the timing of those contributions. Interest crediting rates are reviewed on a semi-annual basis for resetting.

When establishing interest crediting rates for this product, Prudential considers many factors, including current economic and market conditions, the general interest rate environment and both the expected and actual experience of a reference portfolio within the issuer’s general account. These rates are established without the use of a specific formula. The minimum crediting rate under the contract is 1.50%.

	2006		2005
Average earnings yield	4.20	%	3.50	%
Average crediting rate yield	4.20	%	3.50	%

For the periods presented, the average earnings yield is calculated by dividing the earnings credited to the Plan on the last day of the Plan year by the end of the Plan year fair value and then annualizing the result. The average crediting rate yield is calculated by dividing the earnings credited to the Participants on the last day of the Plan year by the end of the Plan year fair value and then annualizing the result. As a result of current stable value product construction, no adjustment will be required to mediate between the average earnings credited to the Plan and the average earnings credited to the Participants.

Key factors that could influence future average interest crediting rates include, but are not limited to: participant directed cash flows; changes in interest rates; total return performance of the securities underlying the contract; or default or credit failures of any of the securities, investment contracts, or other investments held in the Plan.

There are certain events not initiated by Participants that limit the ability of the Plan to transact with the issuer of a GIC at its contract value. Specific coverage provided by each GIC may be different from each issuer, and can be found in the individual GIC contracts held by the Plan. Examples of such events include: the Plan’s failure to qualify under the Internal Revenue Code of 1986 as amended; full or partial termination of the Plan; involuntary termination of employment as a result of a corporate merger, divestiture, spin-off, or other significant business restructuring, which may include early retirement incentive programs or bankruptcy; changes to the administration of the Plan which decreases employee or employer contributions, the establishment of a competing Plan by the plan sponsor, the introduction of a competing investment option, or other Plan amendment that has not been approved by the contract issuers; dissemination of a Participant communication that is designed to induce Participants to transfer assets from this investment option; events resulting in a material and adverse financial impact on the contract issuer, including changes in the tax code, laws or regulations. The Committee does not believe that the occurrence of any of the aforementioned events, which would limit the Plan’s ability to transact with the issuer of a GIC at its contract value with Participants, is probable.

4. Investments

The fair market value of individual investments that represent 5% or more of the Plan’s net assets as of December 31, 2006 or 2005 are as follows:

	December 31,
	2006		2005
Dryden S&P 500 Index Fund	$	64,488,640	$	52,936,584
Guaranteed Income Fund	44,656,683		16,933,272
Heritage Mid Cap Stock Fund	44,255,652		**
Fidelity Puritan Fund	44,156,567		35,283,422
Genzyme Corporation Common Stock	41,852,792		45,952,576
Thornburg International Value Fund	35,810,324		**
Growth Fund of America	32,811,290		24,806,260
Wells Fargo Advantage Small Cap Value Z Fund	24,005,360		**
Large Cap Value/LSV Asset Management Fund	20,748,994		**
Guaranteed Securities Separate Account	N/A		22,913,047
Mid Cap Growth/Artisan Partners Fund	N/A		27,083,727
Small Cap Value/Perkins Wolf McDonnell	N/A		18,197,878

** Less than 5%

During 2006, the Plan’s investments (including gains and losses on investments bought and sold, as well as held during the year) increased in value (including investment income and dividends) by $35,403,173 as follows:

Interest and dividend income
Pooled separate accounts and guaranteed accounts	$	1,529,794
Registered investment companies	2,247,458
Loan interest, net	257,963
Total interest and dividend income	4,035,215
Net appreciation (depreciation) in fair value of investments
Pooled separate accounts	18,804,020
Registered investment companies	18,573,751
Genzyme Corporation Common Stock	(6,009,813		)
Total net appreciation in fair value of investments	31,367,958
Total investment income	$	35,403,173

5. Qualification under the Internal Revenue Code

The IRS determined that the Plan and related trust were designed in accordance with applicable sections of the Code. The most recent favorable determination letter issued to the Plan is dated April 4, 2002.

The Plan has been amended since receiving the determination letter, in accordance with recent tax law changes, including the series of tax acts collectively known as GUST and the Economic Growth and Tax Relief Reconciliation Act of 2001. The Plan administrator and the Plan’s tax counsel believe that the Plan is designed in compliance with the applicable provisions of the Code and ERISA. They are also unaware of anything as to the operation of the Plan that would cause the Plan to not be in compliance with the applicable provisions of the Code and ERISA. Therefore, no provision for income taxes is required.

6. Amendment or Termination of the Plan

Genzyme currently intends to continue the Plan, but reserves the right to terminate it at any time or amend it in any manner advisable. No amendment may adversely affect the nonforfeitable interests of the Participants in their accounts or permit the use or diversion of any part of the Plan other than for the exclusive benefit of the Participants or their beneficiaries (subject to Plan provisions permitting payment of fees and expenses). No merger, consolidation, or transfers of assets or liabilities of the Plan may reduce the Participant’s interest accrued to the date of the merger, consolidation, or transfer.

7. Related Parties

Certain plan investments are separate accounts managed by Prudential. Prudential is the trustee, custodian and record keeper as defined by the Plan and, therefore, these transactions are deemed to be party-in-interest transactions. During the year ended December 31, 2006, the Plan paid Prudential a total of $91,002 of Participant expenses directly out of Participants’ accounts. These expenses consisted primarily of annual base fees, per Participant charges, transaction charges, and fees and commissions on the sale or purchase of common stock. Participant loans are also considered party-in-interest transactions.

During the year ended December 31, 2006, the Plan purchased shares of Genzyme Corporation Common Stock in the amount of $5,665,230, sold shares of Genzyme Corporation Common Stock in the amount of $3,808,955, had net investment depreciation of $6,009,813 and $16,774 of Participant expenses related to Genzyme Corporation Common Stock. The total value of the Plan’s investment in Genzyme Corporation Common Stock was $41,852,792 at December 31, 2006 and $45,952,576 at December 31, 2005

8. Administrative Expenses

Except for Participant expenses, as described in Note 7 above, expenses relating to the general administration of the Plan are paid by Genzyme, the Plan sponsor.

Genzyme Corporation 401(k) Plan
Schedule H, Item 4i

Schedule of Assets (Held at End of Year)

December 31, 2006

(a)	(b) Identity of issue, borrower, lessor or similar party	(c) Description of investment, including maturity date, rate of interest, collateral, par, or maturity value	Units/Shares	(d) Cost	(e) Current value
*	Prudential Guaranteed Income Fund	Guaranteed investment contract	1,135,576	**	$44,656,683

*	Prudential Dryden S&P 500 Index Fund	Pooled separate account	756,177	**	64,488,640

*	Prudential Large Cap Value/LSV Asset Management Fund	Pooled separate account	1,007,854	**	20,748,994

*	Prudential Small Cap Growth/Times Square Fund	Pooled separate account	791,916	**	19,959,993

*	Prudential Mid Cap Value/CRM Fund	Pooled separate account	1,523,283	**	19,184,012

	Thornburg International Value I Fund	Mutual fund	1,234,413	**	35,810,324

	Wells Fargo Advantage Small Cap Value Z Fund	Mutual fund	771,133	**	24,005,360

	PIMCO Total Return Admin Fund	Mutual fund	1,390,995	**	14,438,526

	Fidelity Puritan Fund	Mutual fund	2,211,145	**	44,156,567

	Heritage Mid Cap Stock Fund	Mutual fund	1,598,254	**	44,255,652

	Growth Fund of America	Mutual fund	1,004,632	**	32,811,290

*	Genzyme Corporation	Common stock	679,649	**	41,852,792

*	Participant Loan Fund	Loans with interest rates between 4.00% and 9.00% maturing through 2026		**	5,122,880

		Total			$411,491,713

*		Denotes party-in-interest.
**		Cost information is not required as investments are participant-directed.

SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the administrator of the Genzyme Corporation 401(k) Plan has duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

	GENZYME CORPORATION 401(k) PLAN

	By:	Genzyme Benefit Plans Committee


Date: June 29, 2007	By:	/s/ Zoltan A. Csimma
		Zoltan A. Csimma
		Senior Vice President, Chief Human Resources
		Officer of Genzyme Corporation and Plan Administrator

EXHIBIT INDEX

Exhibit Number		Description

23		Consent of PricewaterhouseCoopers LLP. Filed herewith.

(Mark One):
x		ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended December 31, 2006

OR

o		TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from to

Commission file number 0-14680

	Page
Report of Independent Registered Public Accounting Firm	1

Financial Statements:

Statements of Net Assets Available for Benefits as of December 31, 2006 and 2005	2

Statement of Changes in Net Assets Available for Benefits for the Year Ended December 31, 2006	3

Notes to Financial Statements	4-12

*Supplemental Schedule:**

Schedule of Assets (Held at End of Year) as of December 31, 2006	13

Signature	14

Exhibit Index	15