sc13g


	OMB APPROVAL
	OMB Number: 3235-0145
	Expires: February 28, 2009
	Estimated average burden hours per response...10.4

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934
(Amendment No.__ )*

HELICOS BIOSCIENCES CORPORATION

(Name of Issuer)

Common Stock

(Title of Class of Securities)

42326R 109

(CUSIP Number)

December 31, 2007

(Date of Event Which Requires Filing of This Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

o Rule 13d-1(b)

o Rule 13d-1(c)

þ Rule 13d-1(d)

* The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III, L.P.


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			167,225

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			167,225

WITH:		8	SHARED DISPOSITIVE POWER

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	167,225

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	0.8%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	PN

Page 2 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III-QP, L.P.


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			2,487,091

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			2,487,091

WITH:		8	SHARED DISPOSITIVE POWER

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,487,091

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	11.9%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	PN

Page 3 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III Parallel Fund, LP


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			75,111

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			75,111

WITH:		8	SHARED DISPOSITIVE POWER

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	75,111

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	0.4%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	PN

Page 4 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III GmbH & Co. Beteiligungs KG


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Germany

		5	SOLE VOTING POWER

NUMBER OF			210,189

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			210,189

WITH:		8	SHARED DISPOSITIVE POWER

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	210,189

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	1.0%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	PN

Page 5 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM Asset Management Investors 2003 BVIII LLC


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			48,153

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			0

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			48,153

WITH:		8	SHARED DISPOSITIVE POWER

			0

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	48,153

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	0.2%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	OO

Page 6 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III GP, L.P.


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,936,616*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,936,616*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,936,616*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.0%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	PN

* The shares are held as follows: 2,487,091 by MPM BioVentures III-QP, L.P. (“BV III QP”), 167,225 by MPM BioVentures III, L.P. (“BV III”), 75,111 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 210,189 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). The Reporting Person is the direct general partner of BV III, BV III QP, BV III PF and BV III KG.

Page 7 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) MPM BioVentures III LLC


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	Delaware

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,936,616*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,936,616*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,936,616*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.0%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	OO

* The shares are held as follows: 2,487,091 by MPM BioVentures III-QP, L.P. (“BV III QP”), 167,225 by MPM BioVentures III, L.P. (“BV III”), 75,111 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 210,189 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). The Reporting Person is the indirect general partner of BV III, BV III QP, BV III PF and BV III KG.

Page 8 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Ansbert Gadicke


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

* The shares are held as follows: 2,487,091 by MPM BioVentures III-QP, L.P. (“BV III QP”), 167,225 by MPM BioVentures III, L.P. (“BV III”), 48,153 by MPM Asset Management Investors 2003 BVIII LLC (“BV AM LLC”), 75,111 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 210,189 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). MPM BioVentures III GP, L.P. (“BV III GP”) and MPM BioVentures III LLC (“BV III LLC”) are the direct and indirect general partners of BV III, BV III QP, BV III PF and BV III KG. The Reporting Person is a member of BV III LLC and BV AM LLC. The Reporting Person disclaims beneficial ownership of all such shares except to the extent of his proportionate pecuniary interests therein.

Page 9 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Luke Evnin


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 10 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Nicholas Galakatos


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 11 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Michael Steinmetz


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 12 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Kurt Wheeler


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 13 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Nicholas Simon III


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 14 of 24


CUSIP No.		42326R 109


1	NAME OF REPORTING PERSONS I.R.S. IDENTIFICATION NO(S). OF ABOVE PERSON(S) (ENTITIES ONLY) Dennis Henner


2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (SEE INSTRUCTIONS)
	(a) o
	(b) þ

3	SEC USE ONLY



4	CITIZENSHIP OR PLACE OF ORGANIZATION

	United States

		5	SOLE VOTING POWER

NUMBER OF			0

SHARES		6	SHARED VOTING POWER
BENEFICIALLY
OWNED BY			2,987,769*

EACH		7	SOLE DISPOSITIVE POWER
REPORTING
PERSON			0

WITH:		8	SHARED DISPOSITIVE POWER

			2,987,769*

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

	2,987,769*

10	CHECK IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES (SEE INSTRUCTIONS)

	o

11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)

	14.3%

12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)

	IN

Page 15 of 24

Item 1.

(a)

Name of Issuer

Helicos BioSciences Corporation

(b)

Address of Issuer’s Principal Executive Offices

One Kendall Square
Building 700
Cambridge, MA 02139

Item 2.

(a)

Name of Person Filing

MPM BioVentures III, L.P.
MPM BioVentures III-QP, L.P.
MPM BioVentures III Parallel Fund, L.P.
MPM BioVentures III GmbH & Co. Beteiligungs KG
MPM Asset Management Investors 2003 BVIII LLC
MPM BioVentures III GP, L.P.
MPM BioVentures III LLC
Ansbert Gadicke
Luke Evnin
Nicholas Galakatos
Michael Steinmetz
Kurt Wheeler
Nicholas Simon III
Dennis Henner

(b)

Address of Principal Business Office or, if none, Residence

c/o MPM Capital L.P.
The John Hancock Tower
200 Clarendon Street, 54^th Floor
Boston, MA 02116

(c)

Citizenship

All entities were organized in Delaware, except MPM BioVentures III GmbH & Co. Beteiligungs KG which was organized in Germany. The individuals are United States citizens.

(d)

Title of Class of Securities

Common Stock

(e)

CUSIP Number

42326R 109


Item 3.		If this statement is filed pursuant to §§240.13d-1(b), or 240.13d-2(b) or (c), check whether the person filing is a:

Not applicable

Page 16 of 24

Item 4. Ownership

(a)

Amount Beneficially Owned:


MPM BioVentures III, L.P.	167,225
MPM BioVentures III-QP, L.P.	2,487,091
MPM BioVentures III Parallel Fund, L.P.	75,111
MPM BioVentures III GmbH & Co. Beteiligungs KG	210,189
MPM Asset Management Investors 2003 BVIII LLC	48,153
MPM BioVentures III GP, L.P.	2,936,616	(1)
MPM BioVentures III LLC	2,936,616	(2)
Ansbert Gadicke	2,987,769	(3)
Luke Evnin	2,987,769	(3)
Nicholas Galakatos	2,987,769	(3)
Michael Steinmetz	2,987,769	(3)
Kurt Wheeler	2,987,769	(3)
Nicholas Simon III	2,987,769	(3)
Dennis Henner	2,987,769	(3)

Percent of Class:


MPM BioVentures III, L.P.	0.8	%
MPM BioVentures III-QP, L.P.	11.9	%
MPM BioVentures III Parallel Fund, L.P.	0.4	%
MPM BioVentures III GmbH & Co. Beteiligungs KG	1.0	%
MPM Asset Management Investors 2003 BVIII LLC	0.2	%
MPM BioVentures III GP, L.P.	14.0	%
MPM BioVentures III LLC	14.0	%
Ansbert Gadicke	14.3	%
Luke Evnin	14.3	%
Nicholas Galakatos	14.3	%
Michael Steinmetz	14.3	%
Kurt Wheeler	14.3	%
Nicholas Simon III	14.3	%
Dennis Henner	14.3	%

Page 17 of 24

(b)

Number of shares as to which the person has:

(i)

Sole power to vote or to direct the vote


MPM BioVentures III, L.P.			167,225
MPM BioVentures III-QP, L.P.			2,487,091
MPM BioVentures III Parallel Fund, L.P.			75,111
MPM BioVentures III GmbH & Co. Beteiligungs KG			210,189
MPM Asset Management Investors 2003 BVIII LLC			48,153
MPM BioVentures III GP, L.P.			0
MPM BioVentures III LLC			0
Ansbert Gadicke			0
Luke Evnin			0
Nicholas Galakatos			0
Michael Steinmetz			0
Kurt Wheeler			0
Nicholas Simon III			0
Dennis Henner			0

(ii)

Shared power to vote or to direct the vote


MPM BioVentures III, L.P.	0
MPM BioVentures III-QP, L.P.	0
MPM BioVentures III Parallel Fund, L.P.	0
MPM BioVentures III GmbH & Co. Beteiligungs KG	0
MPM Asset Management Investors 2003 BVIII LLC	0
MPM BioVentures III GP, L.P.	2,936,616	(1)
MPM BioVentures III LLC	2,936,616	(2)
Ansbert Gadicke	2,987,769	(3)
Luke Evnin	2,987,769	(3)
Nicholas Galakatos	2,987,769	(3)
Michael Steinmetz	2,987,769	(3)
Kurt Wheeler	2,987,769	(3)
Nicholas Simon III	2,987,769	(3)
Dennis Henner	2,987,769	(3)

Page 18 of 24

(iii)

Sole power to dispose or to direct the disposition of


MPM BioVentures III, L.P.			167,225
MPM BioVentures III-QP, L.P.			2,487,091
MPM BioVentures III Parallel Fund, L.P.			75,111
MPM BioVentures III GmbH & Co. Beteiligungs KG			210,189
MPM Asset Management Investors 2003 BVIII LLC			48,153
MPM BioVentures III GP, L.P.			0
MPM BioVentures III LLC			0
Ansbert Gadicke			0
Luke Evnin			0
Nicholas Galakatos			0
Michael Steinmetz			0
Kurt Wheeler			0
Nicholas Simon III			0
Dennis Henner			0

(iv)

Shared power to dispose or to direct the disposition of


MPM BioVentures III, L.P.	0
MPM BioVentures III-QP, L.P.	0
MPM BioVentures III Parallel Fund, L.P.	0
MPM BioVentures III GmbH & Co. Beteiligungs KG	0
MPM Asset Management Investors 2003 BVIII LLC	0
MPM BioVentures III GP, L.P.	2,936,616	(1)
MPM BioVentures III LLC	2,936,616	(2)
Ansbert Gadicke	2,987,769	(3)
Luke Evnin	2,987,769	(3)
Nicholas Galakatos	2,987,769	(3)
Michael Steinmetz	2,987,769	(3)
Kurt Wheeler	2,987,769	(3)
Nicholas Simon III	2,987,769	(3)
Dennis Henner	2,987,769	(3)


(1)		The shares are held as follows: 2,487,091 by MPM BioVentures III-QP, L.P. (“BV III QP”), 167,225 by MPM BioVentures III, L.P. (“BV III”), 75,111 by MPM BioVentures III Parallel Fund, L.P. (“BV III PF”) and 210,189 by MPM BioVentures III GmbH & Co. Beteiligungs KG (“BV III KG”). The Reporting Person is the direct general partner of BV III, BV III QP, BV III PF and BV III KG.

(2)		The shares are held as follows: 2,487,091 by BV III QP, 167,225 by BV III, 75,111 by BV III PF and 210,189 by BV III KG. The Reporting Person is the indirect general partner of BV III, BV III QP, BV III PF and BV III KG.

(3)		The shares are held as follows: 2,487,091 by BV III QP, 167,225 by BV III, 48,153 by MPM Asset Management Investors 2003 BVIII LLC (“BV AM LLC”), 75,111 by BV III PF and 210,189 by BV III KG. MPM BioVentures III GP, L.P. (“BV III GP”) and MPM BioVentures III LLC (“BV III LLC”) are the direct and indirect general partners of BV III, BV III QP, BV III PF and BV III KG. The Reporting Person is a member of BV III LLC and BV AM LLC. The Reporting Person disclaims beneficial ownership of all such shares except to the extent of his proportionate pecuniary interests therein.

Item 5. Ownership of Five Percent or Less of a Class

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following o

Item 6. Ownership of More than Five Percent on Behalf of Another Person

Not Applicable

Page 19 of 24


Item 7.		Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on By the Parent Holding Company or Control Person.

Not Applicable


Item 8.		Identification and Classification of Members of the Group

Not Applicable


Item 9.		Notice of Dissolution of a Group

Not Applicable


Item 10.		Certification

Not Applicable

Page 20 of 24

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: February 11, 2008


MPM BIOVENTURES III, L.P.		MPM BIOVENTURES III-QP, L.P.

By:	MPM BioVentures III GP, L.P.,	By:	MPM BioVentures III GP, L.P.,
	its General Partner		its General Partner

By:	MPM BioVentures III LLC,	By:	MPM BioVentures III LLC,
	its General Partner		its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin
	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM BIOVENTURES III PARALLEL FUND, L.P.		MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG

By:	MPM BioVentures III GP, L.P.,	By:	MPM BioVentures III GP, L.P.,
	its General Partner		in its capacity as the Managing Limited Partner

By:	MPM BioVentures III LLC,	By:	MPM BioVentures III LLC,
	its General Partner		its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM ASSET MANAGEMENT INVESTORS 2003 BVIII LLC		MPM BIOVENTURES III GP, L.P.
		By:	MPM BioVentures III LLC,
By:	/s/ Luke Evnin		its General Partner

	Name: Luke Evnin
	Title: Manager
		By:	/s/ Luke Evnin

		Name: Luke Evnin
		Title: Series A Member

MPM BIOVENTURES III LLC

By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke

Name: Luke Evnin			Name: Ansbert Gadicke
Title: Series A Member

Page 21 of 24


By:	/s/ Luke Evnin	By:	/s/ Nicholas Galakatos

	Name: Luke Evnin		Name: Nicholas Galakatos

By:	/s/ Michael Steinmetz	By:	/s/ Kurt Wheeler

	Name: Michael Steinmetz		Name: Kurt Wheeler

By:	/s/ Nicholas Simon III	By:	/s/ Dennis Henner

	Name: Nicholas Simon III		Name: Dennis Henner

EXHIBITS

A: Joint Filing Agreement

Page 22 of 24

EXHIBIT A

JOINT FILING AGREEMENT

In accordance with Rule 13d-1(k) under the Securities Exchange Act of 1934, as amended, the undersigned agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the Common Stock of Helicos BioSciences Corporation and further agree that this agreement be included as an exhibit to such filing. Each party to the agreement expressly authorizes each other party to file on its behalf any and all amendments to such statement. Each party to this agreement agrees that this joint filing agreement may be signed in counterparts.

In evidence whereof, the undersigned have caused this Agreement to be executed on their behalf this 11th day of February, 2008.


MPM BIOVENTURES III, L.P.		MPM BIOVENTURES III-QP, L.P.

By:	MPM BioVentures III GP, L.P.,	By:	MPM BioVentures III GP, L.P.,
	its General Partner		its General Partner

By:	MPM BioVentures III LLC,	By:	MPM BioVentures III LLC,
	its General Partner		its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin
	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM BIOVENTURES III PARALLEL FUND, L.P.		MPM BIOVENTURES III GMBH & CO. BETEILIGUNGS KG

By:	MPM BioVentures III GP, L.P.,	By:	MPM BioVentures III GP, L.P.,
	its General Partner		in its capacity as the Managing Limited Partner

By:	MPM BioVentures III LLC,	By:	MPM BioVentures III LLC,
	its General Partner		its General Partner

By:	/s/ Luke Evnin	By:	/s/ Luke Evnin

	Name: Luke Evnin		Name: Luke Evnin
	Title: Series A Member		Title: Series A Member

MPM ASSET MANAGEMENT INVESTORS 2003 BVIII LLC		MPM BIOVENTURES III GP, L.P.
		By:	MPM BioVentures III LLC,
By:	/s/ Luke Evnin		its General Partner

	Name: Luke Evnin
	Title: Manager
		By:	/s/ Luke Evnin

		Name: Luke Evnin
		Title: Series A Member

Page 23 of 24


MPM BIOVENTURES III LLC

By:	/s/ Luke Evnin	By:	/s/ Ansbert Gadicke

Name: Luke Evnin			Name: Ansbert Gadicke
Title: Series A Member

By:	/s/ Luke Evnin	By:	/s/ Nicholas Galakatos

	Name: Luke Evnin		Name: Nicholas Galakatos

By:	/s/ Michael Steinmetz	By:	/s/ Kurt Wheeler

	Name: Michael Steinmetz		Name: Kurt Wheeler

By:	/s/ Nicholas Simon III	By:	/s/ Dennis Henner

	Name: Nicholas Simon III		Name: Dennis Henner

Page 24 of 24