Exhibit 10.33

                                PROMISSORY NOTE

$400,000.00                                                        May 30, 2000
                              Hayward, California

    FOR VALUE RECEIVED, Brian Metcalf ("Employee"), an employee of Kosan
Biosciences, Inc. ("Company"), hereby unconditionally promises to pay to the
order of Company, in lawful money of the United States of America and in
immediately available funds, the principal sum of Four Hundred Thousand
Dollars ($400,000.00)(the "Loan") due and payable on the date and in the
manner set forth below.

1.  Intent. It is the intent of the parties that the purpose of this Note is
not for consumer, family or household purposes.

2.  Principal Repayment. The outstanding principal amount of the Loan shall
be due and payable on the earlier of the following (the "Maturity Date"): (a)
May 30, 2005; or (b) the date on which Employee voluntarily terminates his
employment relationship with Company.

3.  Interest Rate. Employee further promises to pay interest on the
outstanding principal amount hereof from the date hereof until payment in
full, which interest shall be payable at the rate of 6.3% per annum
compounded annually. Interest shall be due and payable on the Maturity Date
and shall be calculated on the basis of a 360-day year for the actual number
of days elapsed.

4.  Place of Payment; Prepayment. All amounts payable hereunder shall be
payable at the office of Company unless another place of payment shall be
specified in writing by Company. Prepayment is permitted.

5.  Application of Payments. Payment on this Note shall be applied first to
accrued interest, if any, and thereafter to the outstanding principal balance
hereof.

6.  Default. Each of the following events shall be an "Event of Default"
hereunder:

(a)  Employee fails to pay timely any of the principal amount due under this
Note on the date the same becomes due and payable or any accrued interest or
other amounts due under this Note, if any, on the date the same becomes due
and payable, or fails to perform any other obligations hereunder;

(b)  Employee files a petition or action for relief under any bankruptcy,
insolvency or moratorium law or any other law for the relief of, or relating
to, debtors, now or hereafter in effect, or makes any assignment for the
benefit of creditors or takes any action in furtherance of any of the
foregoing;

(c)  An involuntary petition is filed against Employee (unless such petition
is dismissed or discharged within sixty (60) days) under any bankruptcy
statute now or hereafter in effect, or a



custodian, receiver, trustee, assignee for the benefit of creditors (or other
similar official) is appointed to take possession, custody or control of any
property of Employee; or

(d)  Employee's employment by or association with the Company is terminated
for any reason or no reason, including, without limitation, death of Employee.

Upon the occurrence of an Event of Default hereunder, all unpaid principal,
accrued interest and other amounts owing hereunder, if any, shall, at the
option of Company, and, in the case of an Event of Default pursuant to (b) or
(c) above, automatically, be immediately due, payable and collectible by
Company pursuant to applicable law. Notwithstanding the foregoing, if an
Event of Default has occurred under (d) above due to the Company's
termination of Employee's employment with the Company without cause, this
Note shall be converted to a five (5) year note at an interest rate equal to
the Prime Rate plus one percent (1%), compounded annually, and the principal
shall be payable in five equal annual installments, together with interest
thereon payable in arrears calculated on the basis of a 360 day year for the
actual number of days elapsed, beginning one year from such date of
termination of employment. The Prime Rate shall mean the variable rate of
interest, per annum, most recently published in the Money Rate Section of the
New York Edition of The Wall Street Journal, as the "prime rate". If an Event
of Default has occurred under (d) above due to the Company's termination of
Employee's employment with the Company for cause, all unpaid principal and
accrued interest shall be due and payable within six (6) months from such
date of Employee's termination of employment. The Company shall have all
rights and may exercise any remedies available to it under law, successively
or concurrently. Employee expressly acknowledges and agrees that Company
shall have the right to offset any obligations of Employee hereunder against
salaries, bonuses or other amounts that may be payable to Employee by Company.

7.  Waiver. Employee waives presentment and demand for payment, notice of
dishonor, protest and notice of protest of this Note, and shall pay all costs
of collection when incurred, including, without limitation, reasonable
attorneys' fees, costs and other expenses. The right to plead any and all
statutes of limitations as a defense to any demands hereunder is hereby
waived to the full extent permitted by law.

8.  Governing Law. This Note shall be governed by, and construed and enforced
in accordance with, the laws of the State of California, excluding conflict
of laws principles that would cause the application of laws of any other
jurisdiction.

9.  Successors and Assigns. The provisions on this Note shall inure to the
benefit of and be binding on any successor to Employee and shall extend to
any holder hereof. Employee shall not, without the prior written consent of
holder, assign any of its rights or obligations hereunder.

Dated: May 30, 2000



/s/ Brian W. Metcalf
-----------------------------
BRIAN METCALF