##### Table of Contents



---



UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549



---



FORM 10-Q



(Mark one)



|x |  | Quarterly report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934.
|- |  | ----------------------------------------------------------------------------------------

For the quarterly period ended March 31, 2003.



or



| ̈ |  | Transition report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934.
|- |  | -----------------------------------------------------------------------------------------

For the transition period from __________ to __________.



Commission File Number:

000-31633



---



Kosan Biosciences Incorporated

(Exact name of registrant as specified in its charter)



|Delaware                        |  | 94-3217016         
|------------------------------- |  | -------------------
|(State or other jurisdiction of |  | (I.R.S. Employer   
|incorporation or organization)  |  | Identification No.)



3832
Bay Center Place, Hayward, California 94545

(address of principal executive offices)



(510) 732-8400

(Registrants telephone number, including area code)



---



Indicate by check mark whether the registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports), and (2) has been subject to filing requirements for the past 90 days.

YesxNo ̈



Indicate by check mark whether
the registrant is an accelerated filer (as defined in Rules 12b-2 of the Exchange Act).

YesxNo ̈



Indicate the number of shares outstanding of each of the issuers
classes of common stock, as of the latest practicable date: Common Stock, $.001 par value; 25,564,008 shares outstanding at April 30, 2003.



---



---

##### Table of Contents



KOSAN BIOSCIENCES INCORPORATED



Form 10-Q



Quarter Ended March
31, 2003



INDEX



|         |  |                                                                                       |  | Page
|-------- |  | ------------------------------------------------------------------------------------- |  | ----
|PART I.  |  | FINANCIAL INFORMATION                                                                 |  |     
|        
|Item 1:  |  | Condensed Financial Statements and Notes (unaudited):                                 |  |     
|        
|         |  | Condensed Balance Sheets as of March 31, 2003 and December 31, 2002                   |  | 3   
|        
|         |  | Condensed Statements of Operations for the three months ended March 31, 2003 and 2002 |  | 4   
|        
|         |  | Condensed Statements of Cash Flows for the three months ended March 31, 2003 and 2002 |  | 5   
|        
|         |  | Notes to Condensed Financial Statements                                               |  | 6   
|        
|Item 2:  |  | Managements Discussion and Analysis of Financial Condition and Results of Operations |  | 12  
|        
|Item 3:  |  | Quantitative and Qualitative Disclosures About Market Risk                            |  | 25  
|        
|Item 4:  |  | Controls and Procedures                                                               |  | 25  
|        
|PART II. |  | OTHER INFORMATION                                                                     |  |     
|        
|Item 1:  |  | Legal Proceedings                                                                     |  | 27  
|        
|Item 2:  |  | Changes in Securities and Use of Proceeds                                             |  | 27  
|        
|Item 3:  |  | Defaults Upon Senior Securities                                                       |  | 27  
|        
|Item 4:  |  | Submission of Matters to a Vote of Security Holders                                   |  | 27  
|        
|Item 5:  |  | Other Information                                                                     |  | 27  
|        
|Item 6:  |  | Exhibits and Reports on Form 8-K                                                      |  | 27  
|        
|         |  | SIGNATURES                                                                            |  | 29  
|        
|         |  | CERTIFICATIONS                                                                        |  | 30  



2



---

##### Table of Contents



PART I.    FINANCIAL INFORMATION



Item 1:Condensed Financial Statements and Notes



KOSAN BIOSCIENCES INCORPORATED

CONDENSED
BALANCE SHEETS

(in thousands)



|                                           |  | March 31, 2003 |         |   | December 31, 2002 |  
|------------------------------------------ |  | -------------- | ------- | - | ----------------- | -
|                                           |  | (unaudited)    |         |   | (1)               |  
|Assets                                    
|Current assets:                            |  |                |         |   |                   |  
|Cash and cash equivalents                  |  | $              | 23,012  |   |                   | $
|Short-term investments                     |  |                | 30,081  |   |                   |  
|Accounts receivable                        |  |                | 2,913   |   |                   |  
|Prepaid expenses and other current assets  |  |                | 1,182   |   |                   |  
|                                           |  |                |         |   |                   |  
|Total current assets                       |  |                | 57,188  |   |                   |  
|                                          
|Property and equipment, net                |  |                | 5,854   |   |                   |  
|Long-term investments                      |  |                | 26,142  |   |                   |  
|Notes receivable from related parties      |  |                | 380     |   |                   |  
|Other assets                               |  |                | 301     |   |                   |  
|                                           |  |                |         |   |                   |  
|Total assets                               |  | $              | 89,865  |   |                   | $
|                                           |  |                |         |   |                   |  
|Liabilities and Stockholders Equity      
|Current liabilities:                       |  |                |         |   |                   |  
|Accounts payable                           |  | $              | 2,370   |   |                   | $
|Accrued liabilities                        |  |                | 3,781   |   |                   |  
|Current portion of deferred revenue        |  |                | 2,870   |   |                   |  
|Current portion of equipment loans         |  |                | 1,758   |   |                   |  
|                                           |  |                |         |   |                   |  
|Total current liabilities                  |  |                | 10,779  |   |                   |  
|                                          
|Deferred revenue, less current portion     |  |                | 8,646   |   |                   |  
|Equipment loans, less current portion      |  |                | 2,043   |   |                   |  
|                                          
|Stockholders equity:                      |  |                |         |   |                   |  
|Common stock                               |  |                | 26      |   |                   |  
|Additional paid-in capital                 |  |                | 142,243 |   |                   |  
|Notes receivable from stockholders         |  |                | (1,136  | ) |                   |  
|Deferred stock-based compensation          |  |                | (861    | ) |                   |  
|Accumulated other comprehensive income     |  |                | 113     |   |                   |  
|Accumulated deficit                        |  |                | (71,988 | ) |                   |  
|                                           |  |                |         |   |                   |  
|Total stockholders equity                 |  |                | 68,397  |   |                   |  
|                                           |  |                |         |   |                   |  
|Total liabilities and stockholders equity |  | $              | 89,865  |   |                   | $
|                                           |  |                |         |   |                   |  

---

|(1) |  | The balance sheet data at December 31, 2002 has been derived from the audited financial statements at that date.
|--- |  | ----------------------------------------------------------------------------------------------------------------



See accompanying notes.



3



---

##### Table of Contents



KOSAN BIOSCIENCES INCORPORATED

CONDENSED STATEMENTS OF OPERATIONS

(unaudited)

(in thousands, except per share data)



|                                                                     |  | Three Months Ended March 31, |       
|-------------------------------------------------------------------- |  | ---------------------------- | ------
|                                                                     |  | 2003                         |       
|Revenues:                                                            |  |                              |       
|Contract revenue                                                     |  | $                            | 4,347 
|Grant revenue                                                        |  |                              | 911   
|                                                                     |  |                              |       
|Total revenues                                                       |  |                              | 5,258 
|                                                                    
|Operating expenses:                                                  |  |                              |       
|Research and development                                             |  |                              | 6,881 
|General and administrative                                           |  |                              | 1,248 
|                                                                     |  |                              |       
|Total operating expenses                                             |  |                              | 8,129 
|Loss from operations                                                 |  |                              | (2,871
|Other income, net                                                    |  |                              | 289   
|                                                                     |  |                              |       
|Net loss                                                             |  | $                            | (2,582
|                                                                     |  |                              |       
|                                                                    
|Basic and diluted net loss per common share                          |  | $                            | (0.10 
|                                                                     |  |                              |       
|Shares used in computing basic and diluted net loss per common share |  |                              | 25,317



See
accompanying notes.



4



---

##### Table of Contents



KOSAN BIOSCIENCES INCORPORATED

CONDENSED STATEMENTS OF CASH FLOWS

(unaudited)

(in thousands)



|                                                                           |  | Three Months Ended March 31, |        
|-------------------------------------------------------------------------- |  | ---------------------------- | -------
|                                                                           |  | 2003                         |        
|Operating activities                                                       |  |                              |        
|Net loss                                                                   |  | $                            | (2,582 
|Adjustment to reconcile net loss to net cash used in operating
activities: |  |                              |        
|Depreciation and amortization                                              |  |                              | 543    
|Amortization of investment premiums and discounts, net                     |  |                              | 272    
|Amortization of stock-based compensation, net of reversals                 |  |                              | (360   
|Other stock-based compensation                                             |  |                              | 102    
|Realized gain on investment                                                |  |                              |       
|Changes in assets and liabilities:                                         |  |                              |        
|Accounts receivable                                                        |  |                              | 961    
|Prepaid expenses and other current assets                                  |  |                              | (76    
|Other assets and notes receivable from related parties                     |  |                              | 23     
|Accounts payable and accrued liabilities                                   |  |                              | 680    
|Deferred revenue                                                           |  |                              | (255   
|                                                                           |  |                              |        
|Net cash used in operating activities                                      |  |                              | (692   
|                                                                           |  |                              |        
|Investing activities                                                       |  |                              |        
|Acquisition of property and equipment                                      |  |                              | (1,029 
|Purchase of investments                                                    |  |                              | (25,187
|Proceeds from maturity of investments                                      |  |                              | 27,000 
|                                                                           |  |                              |        
|Net cash provided by investing activities                                  |  |                              | 784    
|                                                                           |  |                              |        
|Financing activities                                                       |  |                              |        
|Proceeds from issuance of common stock, net of repurchases                 |  |                              | 408    
|Proceeds from the repayment of notes receivable from stockholders          |  |                              | 28     
|Proceeds from equipment loans                                              |  |                              | 739    
|Principal payments under equipment loans                                   |  |                              | (446   
|                                                                           |  |                              |        
|Net cash provided by (used in) financing activities                        |  |                              | 729    
|                                                                           |  |                              |        
|Net increase in cash and cash equivalents                                  |  |                              | 821    
|Cash and cash equivalents at beginning of period                           |  |                              | 22,191 
|                                                                           |  |                              |        
|Cash and cash equivalents at end of period                                 |  | $                            | 23,012 
|                                                                           |  |                              |        



See
accompanying notes.



5



---

##### Table of Contents



KOSAN BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS

(unaudited)



1.    Organization and Summary of Significant Accounting Policies



Overview



Kosan Biosciences Incorporated (the Company) was incorporated under the laws of the State of California on January 6,
1995 and commenced operations in 1996. In July 2000, the Company was reincorporated under the laws of the state of Delaware. The Company uses its proprietary genetic engineering technologies to develop drug candidates from polyketides, a rich source
of pharmaceutical products.



The Company has
funded its operations primarily through sales of common stock and convertible preferred stock, contract payments under its collaboration agreements, equipment financing arrangements and government grants. Prior to achieving profitable operations,
the Company intends to fund operations through the additional sale of equity securities, strategic collaborations, government grant awards and debt financing.



Basis of Presentation



The accompanying unaudited condensed financial statements have been prepared in accordance with accounting principles generally accepted
in the United States for interim financial information. The information as of March 31, 2003, and for the three months ended March 31, 2003 and 2002, reflects all adjustments (including normal recurring adjustments) that the management of the
Company believes are necessary for a fair presentation of the results for the periods presented. Results for any interim period are not necessarily indicative of results for any future interim period or for the entire year. The accompanying
unaudited condensed financial statements should be read in conjunction with the financial statements and notes thereto included in the Companys Annual Report on Form 10-K for the year ended December 31, 2002.



Use of Estimates



The preparation of financial statements in conformity with
accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the amounts reported in the financial statements and the accompanying notes. Actual results could differ from those
estimates.



Cash Equivalents and Investments



The Company considers all highly liquid investments with a
maturity from date of purchase of three months or less to be cash equivalents. The Company limits its concentration of risk by diversifying its investments among a variety of issuers. All investment securities are classified as available-for-sale
and are recorded at fair value based on quoted market prices, with unrealized gains and losses excluded from earnings and reported in other comprehensive income/(loss). Purchase premiums and discounts are recognized in interest income using the
interest method over the terms of the securities. Realized gains and losses and declines in the fair value that are deemed to be other-than-temporary are reflected in earnings. The cost of securities sold is based on the specific identification
method. For the three months ended March 31, 2002, the Company recorded a $990,000 realized gain related to the full recovery of a previously written-down investment.



The Company holds a restricted investment consisting of a certificate of deposit of approximately $904,000.
This investment is carried at fair value and is restricted as to withdrawal under a letter of credit



6



---

##### Table of Contents



KOSAN
BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS (Continued)

(unaudited)



1.    Organization and Summary of Significant Accounting Policies (Continued)



agreement related to a facility lease. This investment is held in the
Companys name and is included in long-term investments on the Companys financial statements.



Revenue Recognition



The Company recognizes license and other up-front and initial fees pursuant to research and development collaboration agreements over the estimated research and development term of the respective
agreement. Payments related to substantive performance milestones that are at risk at the initiation of an agreement are recognized upon successful completion of a performance milestone event. Contract revenues related to collaborative research and
development efforts are recognized as revenue as the related services are performed. Such payments generally are made based on the number of full-time equivalent researchers assigned to the collaboration project and the related research and
development expenses incurred. Revenues related to government grants are recognized at the time a grant is awarded and as the related research expenses are incurred. Any amounts received in advance of performance are recorded as deferred revenue
until earned.



Research and Development



Research and development expenses consist of costs incurred
for Company-sponsored and collaborative research and development activities. These costs consist primarily of salaries and other personnel-related expenses, stock-based compensation, facility-related expenses, licensing-related expenses,
depreciation of facilities and equipment, lab consumables, clinical trial-related services performed by clinical research organizations and research institutions and other outside service providers.



The continuation of KOS-862 clinical trials has had, and will
continue to have, a significant effect on the Companys research and development expenses. Expenses related to clinical trials generally are accrued based on the level of patient enrollment and activity according to the protocol. The Company
monitors patient enrollment levels and related activity and adjusts estimates accordingly.



Research and development expenses under government grant awards and collaborative agreements approximated the revenue recognized, excluding milestone payments, up-front and initial fees received under
such arrangements.



Net Loss per Share



Basic and diluted net loss per common share has been computed
using the weighted-average number of shares of common stock outstanding during the period, less shares subject to repurchase. Diluted net loss is not presented separately as the Company is in a net loss position and including potentially dilutive
securities in the loss per share computation would be antidilutive.



7



---

##### Table of Contents



KOSAN
BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS (Continued)

(unaudited)



1.    Organization and Summary of Significant Accounting Policies (Continued)



The following table presents the calculation of basic and
diluted net loss per share (in thousands, except per share data):



|                                                                                      |  | Three Months Ended March 31, |       
|------------------------------------------------------------------------------------- |  | ---------------------------- | ------
|                                                                                      |  | 2003                         |       
|Net loss                                                                              |  | $                            | (2,582
|                                                                                      |  |                              |       
|Weighted-average shares of common stock outstanding                                   |  |                              | 25,497
|Less: weighted-average shares subject to repurchase                                   |  |                              | (180  
|                                                                                      |  |                              |       
|Weighted-average shares used in computing basic and diluted net loss per common
share |  |                              | 25,317
|                                                                                      |  |                              |       
|Basic and diluted net loss per common share                                           |  | $                            | (0.10 
|                                                                                      |  |                              |       



Stock-Based
Compensation



The Company accounts for
common stock options granted to employees using the intrinsic value method and, thus, recognizes compensation expense for options granted with exercise prices less than the fair value of the Companys common stock on the date of the grant.
Deferred stock compensation calculated for options granted with exercise prices less than the deemed fair value of the common stock is amortized over the vesting period of the individual options, generally four years, using the graded vesting
method.



Pro forma net loss and net loss per
share information is required by SFAS 123, and has been determined as if the Company had accounted for its employee stock options under the fair value method of that statement. The effects of applying the intrinsic value method for either
recognizing compensation expense or providing pro forma disclosures are not likely to be representative of the effects on net income for future years.



8



---

##### Table of Contents



KOSAN
BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS (Continued)

(unaudited)



1.    Organization and Summary of Significant Accounting Policies (Continued)



The Companys pro forma information follows (in
thousands, except per share amounts):



|                                                                                                          |  | Three Months Ended March 31, |       
|--------------------------------------------------------------------------------------------------------- |  | ---------------------------- | ------
|                                                                                                          |  | 2003                         |       
|Net loss attributable common stockholders, as reported                                                    |  | $                            | (2,582
|Add: Stock-based employee compensation expense included in reported net
loss                              |  |                              | (360  
|Deduct: Stock-based employee compensation expense determined under fair value based
method for all awards |  |                              | 204   
|                                                                                                          |  |                              |       
|Pro forma net loss                                                                                        |  | $                            | (2,738
|                                                                                                          |  |                              |       
|Basic and diluted net loss per common share:                                                              |  |                              |       
|As reported                                                                                               |  | $                            | (0.10 
|Pro forma                                                                                                 |  | $                            | (0.11 



Reclassifications



Certain reclassifications of prior
years balances have been made to conform to the current year presentation. These reclassifications had no effect on prior years net loss or stockholders equity.



2.    Research and Development Agreements



Roche



Effective September 2002, the Company signed a research and development collaboration agreement with
Hoffmann-La Roche, Inc. and F. Hoffmann-La Roche Ltd. (collectively Roche). Under the terms of the agreement, Roche has worldwide exclusive rights to market and sell KOS-862 (Epothilone D) in the field of oncology, and the Company will
co-develop and has the right to co-promote the product in the United States. The Company is entitled to receive payments for the reimbursement of research and development expenditures, funding of a back-up program, achievement of clinical,
regulatory and commercial milestones, development activities and royalties on sales of collaboration products, subject to potential offsets and credits. In addition, the Company has the opportunity to increase its royalties and profit participation
through a buy-in at a later stage of clinical development and by co-promotion of products resulting from the collaboration. For the three months ended March 31, 2003, the Company recognized revenue related to this agreement of approximately $3.5
million.



Johnson & Johnson Pharmaceutical Research and
Development, LLC



Effective September 1998,
the Company signed a collaborative agreement with The R.W. Johnson Pharmaceutical Research Institute, LLC and Ortho-McNeil Pharmaceutical, Inc., both Johnson & Johnson companies. Effective January 1, 2002, the rights and obligations under the
agreement were assigned to Johnson & Johnson Pharmaceutical Research and Development, LLC (J&JPRD), a subsidiary of Ortho-McNeil Pharmaceutical, Inc. In December 2002, the Company amended the collaboration research and
development agreement. Under the terms of the amended agreement, subject to early termination provisions, the research program and funding have been extended until December 28, 2003. J&JPRD will



9



---

##### Table of Contents



KOSAN
BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS (Continued)

(unaudited)



2.    Research and Development Agreements (continued)



take two selected series of compounds forward into preclinical studies. Rights to compounds and technologies developed in the
collaboration that are not related to the compounds under study by J&JPRD, or their close structural analogs, have reverted to the Company. For the three months ended March 31, 2003, the Company recognized revenue of approximately $622,000 in
connection with this agreement, of which $250,000 was related to a non-recurring milestone payment received in connection with this agreement.



License Agreements



The Company has collaborative and license agreements with several academic, government and medical institutions. Included in research and
development expenses were total payments made under these agreements of approximately $88,000 and $18,000 for the three months ended March 31, 2003 and 2002, respectively.



3.    Comprehensive Loss



For the three months ended March 31, 2003 and 2002, comprehensive loss was as follows (in thousands):



|                                                                   |  | Three Months Ended March 31, |       
|------------------------------------------------------------------ |  | ---------------------------- | ------
|                                                                   |  | 2003                         |       
|Net loss                                                           |  | $                            | (2,582
|Unrealized loss on available-for-sale securities                   |  |                              | (39   
|Reclassification of realized gain on available-for-sale securities |  |                              |      
|                                                                   |  |                              |       
|Comprehensive loss                                                 |  | $                            | (2,621
|                                                                   |  |                              |       



4.    Equipment Financing



The Company finances certain equipment and facility improvements under debt obligations. In April 2002, the Company entered into a $3.0 million equipment line of credit agreement. As of March 31, 2003, the Company had
utilized substantially all $3.0 million of the line of credit.



The terms of the loan obligations range from 42 to 49 months. Some of the loans have a balloon payment at the end of the term. The interest rates of each of the loans are fixed at the time of the draw down, with the interest rates
ranging from 6.99% to 13.86%. Obligations under the loans are secured by the assets financed under the loans.



10



---

##### Table of Contents



KOSAN
BIOSCIENCES INCORPORATED

NOTES TO CONDENSED FINANCIAL STATEMENTS (Continued)

(unaudited)



5.    Accrued Liabilities



Accrued liabilities consisted of the following (in thousands):



|                                 |  | March 31, 2003 |       | December 31, 2002
|-------------------------------- |  | -------------- | ----- | -----------------
|Facilities-related               |  | $              | 791   |                  
|Compensation-related             |  |                | 731   |                  
|Professional services            |  |                | 1,052 |                  
|Research and development-related |  |                | 902   |                  
|Other                            |  |                | 305   |                  
|                                 |  |                |       |                  
|                                 |  | $              | 3,781 |                  
|                                 |  |                |       |                  



11



---

##### Table of Contents

Item 2:Managements Discussion and Analysis of Financial Condition and Results of Operations



Forward-Looking Statements



The following discussion of our financial condition and results of operations contains forward-looking statements within the meaning of
Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements relate to future events or our future financial performance. In some cases, you can identify forward-looking
statements by terminology such as may, will, should, expect, plan, anticipate, believe, estimate, predict, potential or continue, the negative of terms like these or other comparable terminology. Actual events or results may differ materially from
those anticipated in these forward-looking statements. All forward-looking statements included in this document are based on information available to us on the date hereof, and we assume no obligation to update any such forward-looking statements.
In evaluating these statements, you should specifically consider various factors, including the risks outlined under the caption Risk Factors That May Affect Results of Operations and Financial Condition set forth at the end of this Item
2, the Risk Factors set forth in our 2002 Annual Report on Form 10-K filed with the SEC and those contained from time to time in our other filings with the SEC. We caution investors that our business and financial performance are subject to
substantial risks and uncertainties.



Overview



We have proprietary gene-engineering
technologies for the manipulation and production of polyketides, a rich source of pharmaceutical products. We use our platform technologies to develop product candidates that target large pharmaceutical markets. In collaboration with Hoffmann-La
Roche, Inc. and F. Hoffmann-La Roche Ltd., collectively Roche, we are testing KOS-862 (Epothilone D), a potential anticancer agent, in Phase I human clinical trials. We are developing geldanamycin derivatives as anticancer agents and are
collaborating with the National Cancer Institute, or NCI, to test one of them, 17-AAG, which is in Phase I human clinical trials. In infectious disease, we have a collaboration with Johnson & Johnson Pharmaceutical Research & Development,
LLC, or J&JPRD, a subsidiary of Ortho-McNeil Pharmaceutical, Inc., focusing on the development of antibiotics. We have additional product development and research programs.



We have incurred significant losses since our inception. As of March 31, 2003, our accumulated deficit was
approximately $72.0 million. We expect to incur additional operating losses over the next several years as we continue to develop our technologies and fund internal product research and development.



Critical Accounting Policies



Revenue Recognition



We recognize license and other up-front and initial fees over
the estimated research and development term of the respective agreement. If the agreement does not have a specified research and development term, we must apply judgment in determining the appropriate timing of recognition. Any changes in our
estimates will result in either an acceleration or further deferral of unamortized revenue. Milestone payments are recognized upon successful completion of a specific scientific or regulatory milestone event. Contract revenues related to
collaborative research and development agreements are recognized as revenues as the related services are performed. Such payments are generally made based on the number of full-time equivalent researchers assigned to the collaboration project and as
the related research and development expenses are incurred. Revenues related to government grant awards are recognized at the time a grant is awarded and as related research expenses are incurred. Any amounts received in advance of performance are
recorded as deferred revenue until earned.



12



---

##### Table of Contents



Stock-Based Compensation



We continue to account for common stock
options granted to employees using the intrinsic value method and, thus, recognize compensation expense for options granted with exercise prices less than the fair value of our common stock on the date of the grant. We recorded total deferred
stock-based compensation of approximately $15.6 million in 2000 and $2.9 million in 1999, which amounts are being amortized to expense using the graded vesting method over the vesting periods of the underlying options, generally four years.
Subsequently, if employees services are terminated during the vesting period, adjustments of previous charges are recognized in the period of termination. We recognized a net credit to stock-based compensation related to employee terminations
of approximately $360,000 for the three months ended March 31, 2003 and an expense of approximately $584,000 for the same period in 2002. Based on deferred stock-based compensation recorded as of March 31, 2003, we expect to record amortization of
deferred stock-based compensation approximately as follows: $669,000 in the remaining nine months of 2003 and $192,000 in 2004.



Stock-based compensation expense for options granted to non-employees has been determined as the fair value of the consideration received
or the fair value of the equity instruments issued, whichever is more reliably measured. We recognized other stock-based compensation for non-employees of approximately $102,000 and $378,000 in the three months ended March 31, 2003 and 2002,
respectively. In addition, assuming no changes, we expect to recognize other stock-based compensation in connection with stock options granted to non-employees of approximately $398,000 in the remaining nine months of 2003, $291,000 in 2004,
$197,000 in 2005 and $69,000 in 2006. The measurement of stock-based compensation to non-employees is subject to periodic adjustment as the underlying securities vest. As such, changes to these measurements could be substantial should we experience
significant changes in our stock price. See Note 1 of our financial statements.



Investments



We
invest in debt and equity securities. The price of these securities is subject to significant volatility. We record an impairment charge when we believe that an investment has experienced a decline in value that is other than temporary. Generally,
we review an investment for impairment if its market value has been below its carrying value for each trading day in a six-month period.



Clinical Trial Accruals



During 2003, our clinical trials of KOS-862 will significantly increase our research and development expenditures. Research and
development expenditures are charged to operations as incurred. Our expenses related to clinical trials are based on estimates of the services received and efforts expended pursuant to contracts with multiple research institutions and clinical
research organizations that conduct and manage clinical trials on our behalf. The financial terms of these agreements are subject to negotiation and variation from contract to contract and may result in uneven payment flows. Payments under the
contracts depend on factors such as the achievement of certain events or the successful enrollment of patients or the completion of portions of the clinical trial or similar conditions. Expenses related to clinical trials generally are accrued based
on the level of patient enrollment and activity according to the protocol. We monitor patient enrollment levels and related activity and adjust our estimates accordingly.



Results of Operations



Revenues



Revenues were approximately $5.3 million for the three months ended March 31, 2003, compared to approximately $1.7 million for the same
period in 2002. The increase was primarily due to approximately $3.5 million in contract revenue recognized under our development and commercialization agreement with Roche, of which approximately $625,000 represented the ratable portion of the
first of two $12.5 million installments of an initial fee that is being recognized over an estimated five-year clinical



13



---

##### Table of Contents



development period. Grant
revenue was approximately $911,000 for the three months ended March 31, 2003, compared to approximately $737,000 for the same period last year. Total contract revenues under our collaboration with J&JPRD were approximately $622,000 for the three
months ended March 31, 2003, compared to approximately $490,000 for the same period in 2002. Included in 2003 contract revenue was a non-recurring $250,000 milestone payment received in connection with the J&JPRD collaboration. The initial term
of the collaboration with J&JPRD has been extended to December 28, 2003, subject to early termination provisions. If we do not maintain or further extend our agreements with Roche and J&JPRD, our revenues will significantly decrease
thereafter, unless we enter into additional collaborations that provide substantial revenues.



Research and Development Expenses



Our research and development expenses consisted primarily of salaries and other personnel-related expenses, fees paid to outside service providers, stock-based compensation, facility-related expenses,
depreciation of facilities and equipment and lab consumables. Research and development expenses increased to approximately $6.9 million for the three months ended March 31, 2003 from approximately $5.9 million for the same period in 2002. This
increase was primarily attributed to the expansion of the clinical development program for KOS-862 (currently in three Phase I clinical trials), for which related expenses are reimbursable by Roche. Further investment supporting our
17-AAG/geldanamycin analog program and other internally funded programs also contributed to the increase. We expect our research and development expenses will increase substantially as KOS-862 advances further into the clinic and as we support our
collaborative research and development programs and advance other in-house research programs into later stages of development.



General and Administrative Expenses



General and administrative expenses were approximately $1.2 million for the three months ended March 31, 2003, compared to approximately
$1.3 million for the same period last year. The decrease was attributed to the net credit to stock-based compensation due to employee terminations, partially offset by higher employee-related costs to support our expanding research and development
activities. We expect our general and administrative expenses will increase in the future to support the continued growth of our research and development efforts.



Other Income, net



Interest income decreased to approximately $372,000 for the three months ended March 31, 2003, from approximately $699,000 for the same
period in 2002. This decrease was attributed to lower average investment balances and lower investment yields associated with the continued decline in interest rates.



Interest expense increased to approximately $83,000 for the three months ended March 31, 2003, from
approximately $78,000 for the same period in 2002. This increase resulted from additional debt financing of property and equipment over the past year. We expect our interest expense will increase in the future resulting from additional property and
equipment-related debt financings.



Included in
other income for the quarter ended March 31, 2002, was a $990,000 realized gain related to the full recovery of a previously written-down investment.



Liquidity and Capital Resources



We have financed our operations from inception primarily through sales of convertible preferred stock and common stock, totaling
approximately $120.6 million in net proceeds, contract payments under our collaboration agreements, equipment financing arrangements and government grant awards. As of March 31, 2003, we had approximately $79.2 million in cash, cash equivalents and
investments, compared to



14



---

##### Table of Contents



approximately $80.5 million as
of December 31, 2002. Our funds are currently invested in U.S. Treasury and government agency obligations and corporate obligations.



Our operating activities used cash of approximately $692,000 for the three months ended March 31, 2003, compared to approximately $3.0
million for the same period in 2002. Our net loss of approximately $2.6 million for the three months ended March 31, 2003 was partially offset by non-cash charges of approximately $557,000 related to stock-based compensation, depreciation and
amortization of investment premiums and discounts and by the timing of cash receipts under our collaboration agreements with Roche and J&JPRD. Cash used for the same period in 2002 was used primarily to fund our net operating loss of
approximately $3.9 million, which included a $990,000 non-cash realized gain on a previously written-down investment, partially offset by non-cash expenses of approximately $1.4 million related to stock-based compensation, depreciation and
amortization of investment premiums and discounts.



Our investing activities, excluding changes in our investments, for the three months ended March 31, 2003, used cash of approximately $1.0 million, compared to approximately $643,000 for the same period in 2002, reflecting facility
improvements and capital expenditures as we continued to enhance and expand our laboratory capabilities.



Cash provided by financing activities was approximately $729,000 for the three months ended March 31, 2003, compared to cash used in
financing activities of approximately $67,000 for the same period in 2002. Financing activities for 2003 included approximately $739,000 in proceeds from equipment loans, partially offset by scheduled payments on existing debt.



In April 2002, we entered into a $3.0 million equipment line
of credit agreement for facility improvements and capital purchases. As of March 31, 2003, we had utilized substantially all $3.0 million of the line of credit. See Note 5 to our financial statements.



We believe that our existing cash, investments and anticipated
cash flow from existing collaborations will be sufficient to support our current operating plan into early 2005. Our future capital uses and requirements depend on numerous forward-looking factors. These factors include, but are not limited to, the
following:



| |  |  | our ability to establish, and the scope of and revenues received under, any new collaborations;
| | - |  | -----------------------------------------------------------------------------------------------



| |  |  | the progress and number of research programs carried out by us;
| | - |  | ---------------------------------------------------------------



| |  |  | the progress and success of preclinical testing and clinical trials of our drug candidates;
| | - |  | -------------------------------------------------------------------------------------------



| |  |  | our ability to maintain or extend our existing collaborations with Roche and J&JPRD;
| | - |  | ------------------------------------------------------------------------------------



| |  |  | the costs and timing of obtaining, enforcing and defending our patent and intellectual rights;
| | - |  | ----------------------------------------------------------------------------------------------



| |  |  | the costs and timing of our facilities expansion;
| | - |  | -------------------------------------------------



| |  |  | the costs and timing of regulatory approvals; and
| | - |  | -------------------------------------------------



| |  |  | expenses associated with unforeseen litigation.
| | - |  | -----------------------------------------------



In addition, we review from time to time potential opportunities to expand our technologies or add to our portfolio of drug candidates. In
the future, we may need further capital in order to acquire or invest in technologies, products or businesses.



We expect that additional financing will be required in the future to fund operations. We expect to finance future cash needs through the
sale of equity securities, strategic collaborations, government grant awards and debt financing. Additional financing or collaboration and licensing arrangements may not be available when needed or, if available, may not be on terms favorable to us
or our stockholders. Insufficient funds may require us to delay, scale back or eliminate some or all of our research or development programs, to lose rights under existing licenses or to relinquish greater or all rights to product candidates at an
earlier stage of development or on less favorable terms than we would otherwise



15



---

##### Table of Contents



choose or may adversely affect
our ability to operate as a going concern. If additional funds are obtained by issuing equity securities, substantial dilution to existing stockholders may result. In addition, see Risk Factors That May Affect Results of Operations and
Financial Condition.



Risk Factors That May Affect
Results of Operations and Financial Condition



You should carefully consider the risks described below, together with all of the other information included in this report, in considering our business and prospects. The risks and uncertainties described below are not the only
ones facing us. Additional risks and uncertainties not presently known to us or that we currently deem immaterial also may impair our business operations. The occurrence of any of the following risks could harm our business, financial condition or
results of operations.



We have a history of net losses
and may never become profitable.



We
commenced operations in 1996 and are still in an early stage of development. We have not commercialized any products, and we have incurred significant losses to date. As of March 31, 2003, we had an accumulated deficit of approximately $72.0
million. To date, our revenues have been solely from collaborations and government grant awards. Our expenses have consisted principally of costs incurred in research and development and from general and administrative costs associated with our
operations. We have incurred net losses since our inception, including a net loss of approximately $2.6 million for the three months ended March 31, 2003. We expect our expenses to increase and to continue to incur operating losses for at least the
next several years as we continue our research and development efforts for our drug candidates. The amount of time necessary to commercialize any of our drug candidates successfully is long and uncertain, and successful commercialization may not
occur at all. As a result, we may never become profitable.



If
our current collaborations are unsuccessful or if conflicts develop with these relationships or under our license agreements, our research and development efforts could be delayed and our revenues could significantly decrease.



We have two corporate research and commercialization
collaborations: with Hoffmann-La Roche, Inc. and F. Hoffmann-La Roche, Ltd. in the field of epothilones, and with Johnson & Johnson Pharmaceutical Research and Development, LLC, a subsidiary of Ortho-McNeil Pharmaceutical, Inc in the field of
ketolide antibiotics. We also have collaborations with, or have licenses to technology and compounds from, several research groups, including Sloan-Kettering Institute for Cancer Research in the field of epothilones, the National Cancer Institute in
the field of geldanamycin analogs and Stanford University in the field of polyketide technology. The agreements permit our collaborators or licensors to terminate the agreement under certain circumstances. We may not be able to maintain or extend
these collaborations or license agreements on acceptable terms, if at all. If we do not maintain, extend or replace these corporate collaborations, our research and development efforts could be delayed and our revenues could significantly decrease.
If we are unable to maintain our research collaborations or if our license agreements are terminated, our research and development efforts could be delayed or terminated or we could lose our rights to use the licensed technology and compounds. Loss
of these rights could also result in termination of our corporate collaborations, under some circumstances.



We do not control the amount and timing of resources that our collaborators devote to our programs or potential products. As a result, we
do not know if our collaborators will dedicate sufficient resources or if the development or commercialization efforts by our corporate collaborators will be successful. We also do not know whether our current collaborative partners or future
collaborative partners, if any, might pursue alternative technologies or develop alternative products either on their own or in collaboration with others, including our competitors, as a means for developing treatments for the diseases targeted by
collaborative arrangements with us. In addition, if a business combination involving our existing corporate collaborators were to occur, the effect could diminish, terminate or cause delays in our corporate collaborations. Should our corporate
partners fail to develop or commercialize a compound or product for which they have rights from us, we may not receive any future milestone payments and will not receive any royalties associated with such compound or product.



16



---

##### Table of Contents



If our
collaborators fail to conduct the collaborative activities successfully and in a timely manner or if they or our licensors were to breach or terminate their agreements with us, the development or commercialization of the affected product candidates
or research program could be delayed or terminated. Conflicts might also arise with collaborators or licensors concerning rights to particular compounds or technologies. If we are unable to resolve these conflicts in our favor, we could lose our
rights to use those compounds or technologies. We are currently in discussions with the Sloan-Kettering Institute for Cancer Research related to whether certain epothilone analogs are licensed to us and if so, the amount owed by us under our
research and license agreement with Sloan-Kettering. We may be required to pay to Sloan-Kettering an amount that is greater than we originally anticipated for the analog research in order to resolve the dispute with Sloan-Kettering as to our right
to develop and commercialize the analogs. If these negotiations do not result in a resolution of these issues that is favorable to us, we may be required to initiate legal proceedings to resolve our rights, and if a court were to disagree with our
interpretation of the license agreement with Sloan-Kettering, we could lose the right to develop and commercialize the analogs. It is also possible that Sloan-Kettering would claim that we have breached our research and license agreement and, as a
result, attempt to terminate the license under which we are developing KOS-862. While we do not believe that a valid basis exists for such a claim of breach, we cannot predict whether or not we would be successful in resolving any such claim. In
addition, if we do not maintain or further extend our agreements with Roche and J&JPRD, our revenues will significantly decrease unless we enter into additional collaborations that provide substantial revenues.



If we fail to enter into new collaborative agreements in the future, our
business and operations would be negatively impacted.



Our strategy depends upon the formation and sustainability of multiple collaborative arrangements and license agreements with third parties in the future. We expect to rely on these arrangements for not only financial resources, but
also for expertise that we expect to need in the future relating to clinical trials, manufacturing, sales and marketing, and for license and technology rights. Although we have established collaborative arrangements and various license agreements,
we do not know if we will be able to establish additional arrangements on favorable terms, or whether current or any future collaborative arrangements will ultimately be successful. There have been, and may continue to be, a significant number of
recent business combinations among large pharmaceutical companies that have resulted, and may continue to result, in a reduced number of potential future corporate collaborators, which may limit our ability to find partners who will work with us in
developing and commercializing our drug candidates. If we do not enter into new collaborative agreements, then our revenues will be reduced, and our drug candidates may not be developed, manufactured or marketed.



Our potential products are in an early stage of development, and
substantial additional effort will be necessary for development.



Our technologies are new, and our drug candidates are in early stages of research and development. We may not develop products that prove to be safe and effective, meet applicable regulatory standards, are capable of being
manufactured at reasonable costs or can be marketed successfully. All of the potential products that we are currently developing will require significant development and investment, including extensive preclinical and clinical testing, before we can
submit any application for regulatory approval.



Our products must satisfy rigorous standards of safety and efficacy before they can be approved by the U.S. Food and Drug Administration, or FDA, and international regulatory authorities for commercial use. We will need to conduct
significant additional research, preclinical testing and clinical trials, before we can file applications with the FDA for product approval. Clinical trials are expensive and have a high risk of failure. In addition, to compete effectively, our
products must be easy to use, cost-effective and economical to manufacture on a commercial scale. We may not achieve any of these objectives. Any of our products may not attain market acceptance. Typically, there is a high rate of attrition for
products in preclinical testing and clinical trials. Also, third parties may develop superior products or have proprietary rights that preclude us from marketing our products. If research and testing is not successful or we fail to obtain regulatory
approval, we will be unable to market and sell our future product candidates.



The progress and results of our animal and human testing are uncertain.



We must provide the FDA and foreign regulatory authorities with clinical data that demonstrates the safety and efficacy of our products before they can be approved for commercial sale. As a result,
commercialization of our product candidates depends upon successful completion of clinical trials. Preclinical testing and clinical development are long, expensive and uncertain processes. It may take us several years to complete our testing, and
failure can occur at any stage of testing. Success in preclinical



17



---

##### Table of Contents



testing and early clinical
trials does not ensure that later clinical trials will be successful, and interim results of trials do not necessarily predict final results. A number of companies in the pharmaceutical industry, including biotechnology companies, have suffered
significant setbacks in advanced clinical trials, even after promising results in earlier trials. None of the product candidates that we have internally developed or licensed have advanced beyond the stage of human testing designed to determine
safety, known as Phase I clinical trials.



We do
not know whether planned clinical trials will begin on time or whether any of our clinical trials will be completed on schedule, or at all. Negative or inconclusive results or adverse medical events during a clinical trial could cause a clinical
trial to be repeated or a program to be terminated. We have two product candidates in human clinical trials for the treatment of cancer. Anticancer drugs generally have a narrow therapeutic window between efficacy and toxicity. If unacceptable
toxicity is observed in clinical trials, the trials may be terminated at an early stage. Drug-related deaths may occur in clinical trials with anticancer drugs, because drugs for the treatment of cancer are typically dangerous and cancer patients
are critically ill.



Completion of clinical
trials may take several years or more. The length of time generally varies substantially according to the type, complexity, novelty and intended use of the drug candidate. Our clinical trials may be suspended at any time, if we or the FDA believe
the patients participating in our studies are exposed to unacceptable health risks. Our commencement and rate of completion of clinical trials may be delayed by many factors, including:



| |  |  | ineffectiveness of the study compound, or perceptions by physicians that the compound is not effective for a particular indication;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------



| |  |  | inability to manufacture sufficient quantities of compound for use in clinical trials;
| | - |  | --------------------------------------------------------------------------------------



| |  |  | failure of the FDA to approve our clinical trial protocols;
| | - |  | -----------------------------------------------------------



| |  |  | slower than expected rate of patient recruitment;
| | - |  | -------------------------------------------------



| |  |  | adverse medical events or the death of patients during a clinical trial for a variety of reasons, including the advanced status of their disease and medical problems
that are not related to our product candidates;
| | - |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | inconclusive or negative results experienced during the clinical trial;
| | - |  | -----------------------------------------------------------------------



| |  |  | third-party clinical investigators failing to perform our clinical trials on our anticipated schedule or consistent with a clinical trial protocol, and other
third-party organizations not performing data collection and analysis in a timely or accurate manner; and
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | government or regulatory delays.
| | - |  | --------------------------------



Any clinical trial may fail to produce results satisfactory to the FDA. Preclinical and clinical data can be interpreted in different
ways, which could delay, limit or prevent regulatory approval.



Our product development costs will increase if we have delays in testing or approvals or if we need to perform more or larger clinical trials than planned. If the delays are significant, our financial results and the commercial
prospects for our products will be harmed, and our ability to become profitable will be delayed.



We do not know whether our existing or any future clinical trials will demonstrate safety and efficacy sufficient to obtain the requisite regulatory approvals or will result in marketable products. Our
failure to adequately demonstrate the safety and efficacy of our products under development will prevent receipt of



18



---

##### Table of Contents



FDA and foreign approvals and,
ultimately, commercialization of our products. If any current or future clinical trials are not successful, our business, financial condition and results of operations will be harmed.



Any inability to protect our proprietary technologies adequately could harm our ability to successfully commercialize
product candidates.



Our commercial success
will depend in part on our ability to obtain patents and maintain adequate protection of other intellectual property for our technologies and products in the United States and other countries. If we do not adequately protect our intellectual
property, competitors may be able to use our technologies and erode or negate any competitive advantage we may have. The laws of some foreign countries do not protect our proprietary rights to the same extent as the laws of the United States, and we
may encounter significant problems in protecting our proprietary rights in these countries.



The patent positions of biotechnology companies, including our patent position, involve complex legal and factual questions, and, therefore, validity and enforceability cannot be predicted with
certainty. Patents may be challenged, deemed unenforceable, invalidated or circumvented. We will be able to protect our proprietary rights from unauthorized use by third parties only to the extent that our proprietary technologies and products are
covered by valid and enforceable patents or are effectively maintained as trade secrets.



The degree of future protection for our proprietary rights is uncertain, and we cannot ensure that:



| |  |  | we or our licensors were the first to make the inventions covered by each of our pending patent applications;
| | - |  | -------------------------------------------------------------------------------------------------------------



| |  |  | we or our licensors were the first to file patent applications for these inventions;
| | - |  | ------------------------------------------------------------------------------------



| |  |  | others will not independently develop similar or alternative technologies or duplicate any of our technologies;
| | - |  | ---------------------------------------------------------------------------------------------------------------



| |  |  | any of our or our licensors pending patent applications will result in issued patents;
| | - |  | ---------------------------------------------------------------------------------------



| |  |  | any patents issued to us or our licensors and collaborators will provide a basis for commercially viable products, will provide us with any competitive advantages or
will not be challenged by third parties;
| | - |  | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | we will develop additional proprietary technologies that are patentable; or
| | - |  | ---------------------------------------------------------------------------



| |  |  | the patents of others will not have an adverse effect on our business.
| | - |  | ----------------------------------------------------------------------



We apply for patents covering both our technologies and drug candidates, as we deem appropriate. However, we
may fail to apply for patents on important technologies or products in a timely fashion or at all. Our existing patents and any future patents we obtain may not be sufficiently broad to prevent others from practicing our technologies or from
developing competing products. In addition, we generally do not control the patent prosecution of technology that we license from others. Accordingly, we are unable to exercise the same degree of control over this intellectual property as we would
over our own.



We rely upon trade secret
protection for our confidential information. We have taken measures to protect our confidential information. However, these measures may not provide adequate protection for our trade secrets. We seek to protect our confidential information by
entering into confidentiality agreements with employees, collaborators and consultants. Nevertheless, we may not be able to protect adequately our trade secrets.



19



---

##### Table of Contents



Litigation or other
proceedings or third-party claims of intellectual property infringement would require us to spend time and money and could prevent us from developing or commercializing products.



Our commercial success depends in part on not infringing the patents and proprietary rights of other parties
and not breaching any licenses that we have entered into with regard to our technologies and products. Others have filed patent applications and issued patents, and in the future are likely to continue to file patent applications and issue patents,
claiming drug candidates that we are developing and genes, gene fragments, compounds and technologies we use or may wish to use. If we wish to use the claimed technology in issued and unexpired patents owned by others, we may need to obtain a
license from another party, enter into litigation or incur the risk of litigation.



The biotechnology industry is characterized by extensive litigation regarding patents and other intellectual property rights. We are aware of patents and published patent applications that, if valid,
and if we are unsuccessful in circumventing or acquiring the rights to these patents, may block our ability to commercialize products based on the drug candidates that we are developing. We cannot be sure that other parties have not filed for or
been issued relevant patents that could affect our ability to obtain patents or to operate as we would like to. Others may sue us in the future to challenge our patent or other intellectual property rights or claim infringement of their patents or
other intellectual property rights or a breach of license agreements, or we may be required to commence legal proceedings to resolve our patent or other intellectual property rights. In particular, we are currently in discussions with the
Sloan-Kettering Institute for Cancer Research related to whether certain epothilone analogs are licensed to us and if so, the amount owed by us under our research and license agreement with Sloan-Kettering. We may be required to pay to
Sloan-Kettering an amount that is greater than we originally anticipated for the analog research in order to resolve the dispute with Sloan-Kettering as to our right to develop and commercialize the analogs. If these negotiations do not result in a
resolution of these issues that is favorable to us, we may be required to initiate legal proceedings to resolve our rights, and if a court were to disagree with our interpretation of the license agreement with Sloan-Kettering, we could lose the
right to develop and commercialize the analogs. It is also possible that Sloan-Kettering would claim that we have breached our research and license agreement and, as a result, attempt to terminate the license under which we are developing KOS-862.
While we do not believe that a valid basis exists for such a claim of breach, we could incur substantial costs and diversion of management and technical personnel in defending ourselves against any such claim, and we cannot predict whether or not we
would be successful in resolving any such claim. An adverse determination in litigation or in an administrative proceeding to which we may become a party could subject us to significant liabilities to others, require us to license disputed rights
from others or require us to cease using the disputed technology.



We are aware of a significant number of patents and patent applications relating to aspects of our technologies and compounds filed by, and issued to, other parties. Others have filed patent applications or have been granted
patents claiming inventions also claimed by us, and we may have to participate in an interference proceeding declared by the relevant patent agency or court to determine priority of invention and, thus, the right to a patent for these inventions in
the United States. For example, we believe one or more interferences may be declared between patents and applications we own or have exclusively licensed and patents and applications owned by Novartis relating to epothilone biosynthetic genes and
Epothilone D; patent applications believed by us to be licensed to Bristol-Myers Squibb relating to epothilones; and patents and applications owned by Abbott Laboratories and Biotica relating to erythromycin polyketide synthase genes, methods for
altering polyketide synthase genes and erythromycin analogs and derivatives. Such a proceeding or a lawsuit in which we are alleged to have infringed an issued patent could result in substantial cost to us even if the outcome is favorable, and if
the outcome is unfavorable, we could be required to license the other partys rights, at terms that may be unfavorable to us, or cease using the technology. Even if successful on priority grounds, an interference may result in loss of claims
based on patentability grounds raised in the interference. Although patent and intellectual property disputes in the biotechnology area are often settled through licensing or similar arrangements, costs associated with these arrangements may be
substantial and could include ongoing royalties. Furthermore, we cannot be certain that a license would be available to us on satisfactory terms, if at all.



Other parties may obtain patents in the future and claim that the use of our technologies infringes these patents or that we are employing
their proprietary technology without authorization. We could incur substantial costs and diversion of management and technical personnel in defending ourselves against any claims that the use of our technologies infringes any patents, defending
ourselves against any claims that we are employing any proprietary technology without authorization or enforcing our patents against others. Furthermore, parties making claims against us may be able to obtain injunctive or other equitable relief
that could effectively block our ability to develop, commercialize and sell products, and could result in the award of substantial damages against us. In the event of a successful claim of infringement against us, we may be required to:



| |  |  | pay substantial damages;
| | - |  | ------------------------



| |  |  | stop using certain products and methods;
| | - |  | ----------------------------------------



20



---

##### Table of Contents



| |  |  | develop non-infringing products and methods; and
| | - |  | ------------------------------------------------



| |  |  | obtain one or more licenses from other parties.
| | - |  | -----------------------------------------------



We may not be able to obtain licenses from other parties at a reasonable cost, if at all. In that event, we could encounter substantial
delays in product introductions while we attempt to develop alternative methods and products, which we may not be able to accomplish.



Litigation or the failure to obtain licenses could prevent us from commercializing products.



We rely on third parties to conduct our clinical trials, and those third
parties may not perform satisfactorily.



If
third parties do not successfully carry out their contractual duties or meet expected deadlines, we will not be able to obtain regulatory approvals for our product candidates and will not be able to successfully commercialize our product candidates
for targeted diseases. We do not have the ability to independently conduct clinical trials for our products, and we rely on third parties such as contract research organizations, medical institutions and clinical investigators to perform this
function. If these third parties do not perform satisfactorily, our clinical trials may be extended or delayed. We may not be able to locate any necessary acceptable replacements or enter into favorable agreements with them, if at all.



If we are unable to recruit and retain skilled employees, we may not be
able to achieve our objectives.



Retaining
our current employees and recruiting qualified scientific personnel to perform future research and development work will be critical to our success. Competition is intense for experienced scientists, and we may not be able to retain or recruit
sufficient skilled personnel to allow us to pursue collaborations and develop our products and core technologies to the extent otherwise possible. Additionally, we are highly dependent on the principal members of our management and scientific staff,
such as our two co-founders, the loss of whose services would adversely impact the achievement of our objectives. Although we maintain, and are the beneficiary of, $1.0 million key-man life insurance policies for the lives of each of our two
co-founders, Daniel V. Santi, M.D., Ph.D., our chairman and chief executive officer, and Chaitan S. Khosla, Ph.D., a director and consultant, we do not believe the proceeds would be adequate to compensate us for their loss.



We face intense competition from large pharmaceutical companies,
biotechnology companies and academic groups.



We face, and will continue to face, intense competition from organizations such as large biotechnology and pharmaceutical companies, as well as academic and research institutions and government agencies, that are pursuing competing
technologies and products. These organizations may develop technologies or products that are superior alternatives to ours. For example, other epothilones, including those being developed by Bristol-Myers Squibb and Novartis AG, are reported to be
in Phase II clinical trials in cancer patients. Further, our competitors in the polyketide gene-engineering field may be more effective at implementing their technologies to develop commercial products. Some of these competitors have entered into
collaborations with leading companies within our target markets to produce polyketides for commercial purposes.



Any products that we develop through our technologies will compete in multiple, highly competitive markets. Development of pharmaceutical
products requires significant investment and resources. Many of the organizations competing with us in the markets for such products have greater capital resources, research and development and marketing staffs, facilities and capabilities, and
greater experience in



21



---

##### Table of Contents



discovery and developing
drugs, obtaining regulatory approvals and product manufacturing and marketing. Accordingly, our competitors may be able to develop technologies and products more easily, which would render our technologies and products and those of our collaborators
obsolete and noncompetitive.



If we face liability claims in
clinical trials of a drug candidate, these claims will divert our managements time and we will incur litigation costs.



We face an inherent business risk of clinical trial liability claims in the event that the use or misuse of our potential products results
in personal injury or death. We may experience clinical trial liability claims if our drug candidates are misused or cause harm before regulatory authorities approve them for marketing. Even though we have obtained clinical trial liability
insurance, it may not be sufficient to cover claims that may be made against us. Clinical trial liability insurance is expensive, difficult to obtain and may not be available in the future on acceptable terms, if at all. Any claims against us,
regardless of their merit, could materially and adversely affect our financial condition, because litigation related to these claims would strain our financial resources in addition to consuming the time and attention of our management. If we are
sued for any injuries caused by our products, our liability could exceed our total assets.



We use hazardous chemicals and radioactive and biological materials in our business. Any claims relating to improper handling, storage or disposal of these materials could be time consuming and
costly.



Our research and development
processes involve the controlled use of hazardous materials, including hazardous chemicals and radioactive and biological materials. Some of these materials may be novel, including bacteria with novel properties and bacteria that produce
biologically active compounds. Our operations also produce hazardous waste products. We cannot eliminate the risk of accidental contamination or discharge and any resultant injury from these materials. Federal, state and local laws and regulations
govern the use, manufacture, storage, handling and disposal of these materials. We believe that our current operations comply in all material respects with these laws and regulations. We could be subject to civil damages in the event of an improper
or unauthorized release of, or exposure of individuals to, hazardous materials. In addition, we could be sued for injury or contamination that results from our use or the use by third parties or our collaborators of these materials, and our
liability may exceed our total assets. Compliance with environmental laws and regulations may be expensive, and current or future environmental regulations may impair our research, development or commercialization efforts.



We have a stockholders rights plan and anti-takeover provisions in our
corporate charter documents that may result in outcomes with which you do not agree.



Our board of directors has the authority to issue up to 10,000,000 shares of preferred stock and to determine the rights, preferences, privileges and restrictions of those shares without further vote
or action by our stockholders. The rights of the holders of any preferred stock that may be issued in the future may adversely affect the rights of the holders of common stock. The issuance of preferred stock could make it more difficult for third
parties to acquire a majority of our outstanding voting stock.



Our certificate of incorporation provides for staggered terms for the members of the board of directors and prevents our stockholders from acting by written consent. These provisions and other provisions of our bylaws and of Delaware
law applicable to us could delay or make more difficult a merger, tender offer or proxy contest involving us. This could reduce the price that investors might be willing to pay for shares of our common stock and result in the market price being
lower than it would be without these provisions. In addition, these provisions may frustrate or prevent any attempts by our stockholders to replace or



22



---

##### Table of Contents



remove our current management
by making it more difficult for stockholders to replace members of our board of directors. Because our board of directors is responsible for appointing the members of our management team, these provisions could in turn affect any attempt by our
stockholders to replace current members of our management team.



We have adopted a rights agreement under which all stockholders have the right to purchase shares of a new series of preferred stock at an exercise price of $70.00 per one one-hundredth of a share, if a person acquires more than 20%
of our common stock. The rights plan could make it more difficult for a person to acquire a majority of our outstanding voting stock. The rights plan could also reduce the price that investors might be willing to pay for shares of our common stock
and result in the market price being lower than it would be without the rights plan. In addition, the existence of the rights plan itself may deter a potential acquiror from acquiring us. As a result, either by operation of the rights plan or by its
potential deterrent effect, mergers and acquisitions of us that our stockholders may consider in their best interests may not occur.



Some of our existing stockholders can exert control over us and may not make decisions that are in the best interest of all stockholders.



Our officers, directors and their
affiliates together control approximately 31% of our outstanding common stock. As a result, these stockholders, if they act together, are able to exert a significant degree of influence over our management and affairs and over matters requiring
stockholder approval, including the election of directors and approval of significant corporate transactions. This concentration of ownership may delay or prevent a change in control of us and might affect the market price of our common stock, even
when a change may be in the best interests of all stockholders. In addition, the interests of this concentration of ownership may not always coincide with our interests or the interests of other stockholders and accordingly, they could cause us to
enter into transactions or agreements which we would not otherwise consider.



Our stock price has been, and may continue to be, extremely volatile.



The trading price of our common stock has been, and is likely to continue to be, highly volatile and could be subject to wide fluctuations in price in response to various factors, many of which are
beyond our control, including:



| |  |  | announcements of technological developments in research by us or our competitors;
| | - |  | ---------------------------------------------------------------------------------



| |  |  | delay or failure in initiating, conducting, completing or analyzing clinical trials or unsatisfactory design or results of these trials by us or our competitors;
| | - |  | -----------------------------------------------------------------------------------------------------------------------------------------------------------------



| |  |  | achievement of regulatory approvals;
| | - |  | ------------------------------------



| |  |  | new products or services introduced or announced by us or our competitors;
| | - |  | --------------------------------------------------------------------------



| |  |  | changes in financial estimates by securities analysts;
| | - |  | ------------------------------------------------------



| |  |  | announcements of departures or departures of key personnel;
| | - |  | -----------------------------------------------------------



| |  |  | announcements of litigation or an unfavorable outcome in litigation; and
| | - |  | ------------------------------------------------------------------------



| |  |  | sales of our common stock.
| | - |  | --------------------------



In addition, the stock market in general, and the Nasdaq National Market and the market for biotechnology companies in particular, has
experienced extreme price and volume fluctuations that have often been unrelated or disproportionate to the operating performance of those companies. These broad market and industry factors may seriously harm the market price of our common stock,
regardless of our operating performance. In the past, following periods of volatility in the market price of a companys securities, securities class-action litigation has often been instituted against that company. If this type of litigation
were instituted against us, we would be faced with substantial costs and managements attention



23



---

##### Table of Contents

and resources would be diverted, which could in turn seriously harm our business, financial condition and results of operations.



We expect that our quarterly results of operations will
fluctuate, and this fluctuation could cause our stock price to decline, creating investor losses.



Our quarterly operating results have fluctuated in the past and are likely to do so in the future. These fluctuations could cause our
stock price to fluctuate significantly or decline. Some of the factors that could cause our operating results to fluctuate include:



| |  |  | expiration or termination of research contracts with collaborators or government research grants, which may not be renewed or replaced;
| | - |  | ---------------------------------------------------------------------------------------------------------------------------------------



| |  |  | the success rate of our discovery efforts leading to milestones and royalties;
| | - |  | ------------------------------------------------------------------------------



| |  |  | the timing and willingness of collaborators to commercialize our products; and
| | - |  | ------------------------------------------------------------------------------



| |  |  | general and industry specific economic conditions, which may affect our collaborators research and development expenditures.
| | - |  | -----------------------------------------------------------------------------------------------------------------------------



A large portion of our expenses is relatively fixed, including
expenses for facilities, equipment and personnel. Accordingly, if revenues decline or do not grow due to expiration or termination of research contracts or government research grants, failure to obtain new contracts or other factors, we may not be
able to reduce our operating expenses correspondingly. In addition, we expect operating expenses to continue to increase. Failure to achieve anticipated levels of revenues could therefore significantly harm our operating results for a particular
fiscal period.



Due to the possibility of
fluctuations in our revenues and expenses, we believe that quarter-to-quarter comparisons of our operating results are not a good indication of our future performance. Our operating results in some quarters may not meet the expectations of stock
market analysts and investors. In that case, our stock price would probably decline.



If we fail to obtain the capital necessary to fund our operations, we will be unable to successfully develop products.



Additional financing will be required in the future to fund operations. We do not know whether additional financing will be available when
needed, or that, if available, we will obtain financing on terms favorable to our stockholders or us. We have consumed substantial amounts of cash to date and expect capital outlays and operating expenditures to increase over the next several years
as we expand our infrastructure and research and development activities.



We believe that our existing cash and investment securities and anticipated cash flow from existing collaborations will be sufficient to support our current operating plan into early 2005. We have based this estimate on
assumptions that may prove to be wrong. Our future capital requirements depend on many factors that affect our research, development, collaboration and sales and marketing activities. See Liquidity and Capital Resources, above.



We may raise additional financing through public
or private equity offerings, debt financings or additional corporate collaboration and licensing arrangements. To the extent we raise additional capital by issuing equity securities, our stockholders may experience dilution. To the extent that we
raise additional funds through collaboration and licensing arrangements, it may be necessary to relinquish some rights to our technologies or product candidates, or grant licenses on terms that are not favorable to us. If adequate funds are not
available, we will not be able to continue developing our products.



24



---

##### Table of Contents



Item 3:Quantitative and Qualitative Disclosures About Market Risk



Interest Rate Risk



The primary objective of our investment activities is to preserve principal while at the same time maximize the income we receive from our
investments without significantly increasing risk. Some of the securities that we invest in may have market risk. This means that a change in prevailing interest rates may cause the principal amount of the investment balance to fluctuate. To
minimize this risk in the future, we intend to maintain our portfolio of cash equivalents and investments in a variety of securities, including commercial paper, money market funds, government and non-government debt securities and investment-grade
corporate obligations.



The following table
represents the fair value balance of our cash, cash equivalents and short-term and long-term investments that are subject to interest rate risk by year of expected maturity and average interest rates as of March 31, 2003 (dollars in thousands):



|                        |  | 2003 |        |   | 2004 |   |        | 2005 | 
|----------------------- |  | ---- | ------ | - | ---- | - | ------ | ---- | 
|Cash & cash equivalents |  | $    | 23,012 |   |      |   |       |      | 
|Average interest rates  |  |      | 1.19   | % |      |   |        |      | 
|                       
|Short-term investments  |  |      | 21,957 |   |      | $ | 8,124  |      | 
|Average interest rates  |  |      | 1.90   | % |      |   | 2.54   | %    | 
|                       
|Long-term investments   |  |      |       |   |      |   | 23,646 |      | 
|Average interest rates  |  |      |        |   |      |   | 1.73   | %    | 



We did
not hold derivative instruments as of March 31, 2003, and we have never held such instruments in the past. In addition, we had outstanding debt, consisting of borrowings under equipment financings, of $3.8 million as of March 31, 2003, with a range
of interest rates from 6.99% to 13.86%.



Item 4:Controls and Procedures



Evaluation of Disclosure Controls and Procedures.    Based on their evaluation as of a date within 90 days of
the filing date of this report, our principal executive officer and principal financial officer have concluded that Kosans disclosure controls and procedures (as defined in Rules 13a-14(c) and 15d-14(c) under the Securities Exchange Act of
1934, as amended (the Exchange Act)) are sufficiently effective to ensure that the information required to be disclosed by Kosan in the reports that we file under the Exchange Act is gathered, analyzed and disclosed with adequate
timeliness, accuracy and completeness.



Changes in Internal Controls.    There have been no significant changes in our internal controls or in other factors that could significantly affect these controls subsequent to the date of the evaluation
referred to above, nor were there any significant deficiencies or material weaknesses in Kosans internal controls. Accordingly, no corrective actions were required or undertaken.



Limitations on the Effectiveness of Controls.    Kosans management,
including our chief executive officer and chief financial officer, does not expect that our disclosure controls and procedures or our internal controls will prevent all error and all fraud. A control system, no matter how well conceived and
operated, can provide only reasonable, not absolute, assurance that the objectives of the control system are met. Further, the design of a control system must reflect the fact that there are resource constraints, and the benefits of controls must be
considered relative to their costs. Because of the inherent limitations in all control systems, no evaluation of controls can provide absolute assurance that all control issues and instances of fraud, if any, within the company have been detected.
These inherent limitations include the



25



---

##### Table of Contents



realities that judgments in
decision-making can be faulty, and that breakdowns can occur because of simple error or mistake. Additionally, controls can be circumvented by the individual acts of some persons, by collusion of two or more people or by management override of the
control. The design of any system of controls also is based in part upon certain assumptions about the likelihood of future events, and there can be no assurance that any design will succeed in achieving its stated goals under all potential future
conditions; over time, controls may become inadequate because of changes in conditions, or the degree of compliance with the policies or procedures may deteriorate. Because of the inherent limitations in a cost-effective control system,
misstatements due to error or fraud may occur and not be detected.



26



---

##### Table of Contents



PART II.    OTHER INFORMATION



Item 1:Legal Proceedings



Not applicable.



Item 2:Changes in Securities and Use of Proceeds



d)    Use of Proceeds



Our initial public offering of common stock was effected in October 2000, in which we sold
5,750,000 shares of our common stock.



The net proceeds of the 5,750,000 shares registered and sold were approximately $73.4 million. We paid a total of approximately $5.6 million in underwriting discounts and commissions and approximately $1.5 million in other costs and
expenses in connection with the offering. None of the expenses were paid, directly or indirectly, to directors, officers or persons owning ten percent or more of our common stock.



Of the net offering proceeds, through March 31, 2003, approximately $3.7 million had been
used to purchase property and equipment and approximately $18.1 million had been used for general corporate purposes. We intend to use the remaining net proceeds for advancing our drug candidates through preclinical and later stage development,
discovering or acquiring new drug candidates, expanding our technology platform, capital expenditures, working capital, general corporate purposes and possible future acquisitions. Pending such uses, the balance has been invested in U.S. Treasury
and government agency obligations and corporate obligations.



Item 3:Defaults Upon Senior Securities



Not applicable.



Item 4:Submission of Matters to a Vote of Security Holders



Not applicable.



Item 5:Other Information



Not applicable.



Item 6:Exhibits and Reports on Form 8-K



(a)    Exhibits:



|Exhibit No. |  |                                                                            
|----------- |  | ---------------------------------------------------------------------------
|           
|3.1         |  | Amended and Restated Certificate of Incorporation.(1)                      
|           
|3.2         |  | Bylaws of Registrant.(2)                                                   
|           
|4.1         |  | Form of Specimen Common Stock Certificate.(2)                              
|           
|99.1        |  | Certification Pursuant to Section 906 of the Sarbanes-Oxley Act of
2002.(3)



(b)    Reports on Form 8-K



None.





---

|(1) |  | Incorporated herein by reference to an exhibit of our Quarterly Report on Form 10-Q for the period ended June 30, 2001.
|--- |  | -----------------------------------------------------------------------------------------------------------------------



27



---

##### Table of Contents



|(2) |  | Incorporated herein by reference to an exhibit of our Registration Statement on Form S-1, Registration No. 333-33732.
|--- |  | ---------------------------------------------------------------------------------------------------------------------

|(3) |  | This certification accompanies the Quarterly Report on Form 10-Q to which it relates, pursuant to Section 906 of the Sarbanes Oxley Act of 2002, and is
not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of Kosan Biosciences Incorporated under the Securities Act or the Exchange Act (whether made before or after the date of the
Quarterly Report on Form 10-Q), irrespective of any general incorporation language contained in such filing.
|--- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------



28



---

##### Table of Contents



SIGNATURES



Pursuant
to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.



|             |  |  |  | Kosan Biosciences Incorporated
|------------ |  |  |  | ------------------------------
|            
|May 14, 2003 |  |  |  | By:                           
|             |  |  |  |                               
|            
|May 14, 2003 |  |  |  | By:                           
|             |  |  |  |                               



29



---

##### Table of Contents



CERTIFICATION



I,
Daniel V. Santi, M.D., Ph.D., Chief Executive Officer of Kosan Biosciences Incorporated, certify that:



1.    I have reviewed this Quarterly Report on Form 10-Q of Kosan Biosciences Incorporated;



2.    Based on my knowledge, this
Quarterly Report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the
period covered by this Quarterly Report;



3.    Based on my knowledge, the financial statements, and other financial information included in this Quarterly Report, fairly present in all material respects the financial condition, results of operations and
cash flows of the registrant as of, and for, the periods presented in this Quarterly Report;



4.    The registrants other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules
13a-14 and 15d-14) for the registrant and we have:



a)    designed such disclosure controls and procedures to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities,
particularly during the period in which this Quarterly Report is being prepared;



b)    evaluated the effectiveness of the registrants disclosure controls and procedures as of a date within 90 days prior to the filing date of this Quarterly Report (the
Evaluation Date); and



c)    presented in this Quarterly Report our conclusions about the effectiveness of the disclosure controls and procedures based on our evaluation as of the Evaluation Date;



5.    The registrants other
certifying officers and I have disclosed, based on our most recent evaluation, to the registrants auditors and the audit committee of registrants board of directors (or persons performing the equivalent function):



a)    all significant deficiencies in the
design or operation of internal controls which could adversely affect the registrants ability to record, process, summarize and report financial data and have identified for the registrants auditors any material weaknesses in internal
controls; and



b)    any
fraud, whether or not material, that involves management or other employees who have a significant role in the registrants internal controls; and



6.    The registrants other certifying officers and I have indicated in this Quarterly Report whether or not
there were significant changes in internal controls or in other factors that could significantly affect internal controls subsequent to the date of our most recent evaluation, including any corrective actions with regard to significant deficiencies
and material weaknesses.



|                  
|------------------
|Date: May 14, 2003
|                  



30



---

##### Table of Contents



CERTIFICATION



I, Susan M.
Kanaya, Senior Vice President, Finance, Chief Financial Officer and Secretary of Kosan Biosciences Incorporated, certify that:



1.    I have reviewed this Quarterly Report on Form 10-Q of Kosan Biosciences Incorporated;



2.    Based on my knowledge, this
Quarterly Report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the
period covered by this Quarterly Report;



3.    Based on my knowledge, the financial statements, and other financial information included in this Quarterly Report, fairly present in all material respects the financial condition, results of operations and
cash flows of the registrant as of, and for, the periods presented in this Quarterly Report;



4.    The registrants other certifying officers and I are responsible for establishing and maintaining disclosure controls and procedures (as defined in Exchange Act Rules
13a-14 and 15d-14) for the registrant and have:



a)    designed such disclosure controls and procedures to ensure that material information relating to the registrant, including its consolidated subsidiaries, is made known to us by others within those entities,
particularly during the period in which this Quarterly Report is being prepared;



b)    evaluated the effectiveness of the registrants disclosure controls and procedures as of a date within 90 days prior to the filing date of this Quarterly Report (the
Evaluation Date); and



c)    presented in this Quarterly Report our conclusions about the effectiveness of the disclosure controls and procedures based on our evaluation as of the Evaluation Date;



5.    The registrants other
certifying officers and I have disclosed, based on our most recent evaluation, to the registrants auditors and the audit committee of registrants board of directors (or persons performing the equivalent function):



a)    all significant deficiencies in the
design or operation of internal controls which could adversely affect the registrants ability to record, process, summarize and report financial data and have identified for the registrants auditors any material weaknesses in internal
controls; and



b)    any
fraud, whether or not material, that involves management or other employees who have a significant role in the registrants internal controls; and



6.    The registrants other certifying officers and I have indicated in this Quarterly Report whether or not
there were significant changes in internal controls or in other factors that could significantly affect internal controls subsequent to the date of our most recent evaluation, including any corrective actions with regard to significant deficiencies
and material weaknesses.



|                  
|------------------
|Date: May 14, 2003
|                  





31



---

##### Table of Contents



EXHIBIT INDEX



|Exhibit No. |  |                                                                            
|----------- |  | ---------------------------------------------------------------------------
|           
|3.1         |  | Amended and Restated Certificate of Incorporation.(1)                      
|           
|3.2         |  | Bylaws of Registrant.(2)                                                   
|           
|4.1         |  | Form of Specimen Common Stock Certificate.(2)                              
|           
|99.1        |  | Certification Pursuant to Section 906 of the Sarbanes-Oxley Act of
2002.(3)

---

|(1) |  | Incorporated herein by reference to an exhibit of our quarterly report on Form 10-Q for the period ended June 30, 2001.
|--- |  | -----------------------------------------------------------------------------------------------------------------------

|(2) |  | Incorporated herein by reference to an exhibit of our Registration Statement on Form S-1, Registration No. 333-33732.
|--- |  | ---------------------------------------------------------------------------------------------------------------------

|(3) |  | This certification accompanies the Quarterly Report on Form 10-Q to which it relates, pursuant to Section 906 of the Sarbanes Oxley Act of 2002, and is
not deemed filed with the Securities and Exchange Commission and is not to be incorporated by reference into any filing of Kosan Biosciences Incorporated under the Securities Act or the Exchange Act (whether made before or after the date of the
Quarterly Report on Form 10-Q), irrespective of any general incorporation language contained in such filing.
|--- |  | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------