ONYX PHARMACEUTICALS INC
S-3, 1998-04-02
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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<PAGE>

     AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON APRIL 2, 1998
                                                          REGISTRATION NO. 333-
- -------------------------------------------------------------------------------

                      SECURITIES AND EXCHANGE COMMISSION
                            WASHINGTON, D.C.  20549
                                       
                           ------------------------
                                   FORM S-3
                            REGISTRATION STATEMENT
                                     UNDER
                          THE SECURITIES ACT OF 1933

                           ------------------------
                          ONYX PHARMACEUTICALS, INC.
            (Exact name of registrant as specified in its charter)

<TABLE>
<CAPTION>
       DELAWARE                               2836                                94-3154463
<S>                                 <C>                                 <C>
(State or other jurisdiction of      (Primary Standard Industrial        (I.R.S. Employer Identification 
 incorporation or organization)       Classification Code Number)                    Number)

</TABLE>

                              3031 RESEARCH DRIVE
                             RICHMOND, CALIFORNIA
                                (510) 222-9700
                                       
  (Address, including zip code, and telephone number, including area code, of
                   registrant's principal executive offices)

                           ------------------------

                              HOLLINGS C. RENTON
                     PRESIDENT AND CHIEF EXECUTIVE OFFICER
                          ONYX PHARMACEUTICALS, INC.
                              3031 RESEARCH DRIVE
                              RICHMOND, CA  94806
(Name, address, including zip code, and telephone number, including area code,
                             of agent for service)
                                       
                                  COPIES TO:

                             ROBERT L. JONES, ESQ.
                              COOLEY GODWARD LLP
                             FIVE PALO ALTO SQUARE
                              3000 EL CAMINO REAL
                          PALO ALTO, CALIFORNIA 94306
                                (415) 843-5000

                           ------------------------

       APPROXIMATE DATE OF COMMENCEMENT OF PROPOSED SALE TO THE PUBLIC:
  AS SOON AS PRACTICABLE AFTER THE REGISTRATION STATEMENT BECOMES EFFECTIVE.

                           ------------------------

     If the only securities being registered on this Form are being offered 
pursuant to dividend or interest reinvestment plans, please check the 
following box. / /
     If any of the securities being registered on this Form are to be offered 
on a delayed or continuous basis pursuant to Rule 415 under the Securities 
Act of 1933, other than securities offered only in connection with dividend 
or interest reinvestment plans, check the following box.  /x/
     If this form is filed to register additional securities for an offering 
pursuant to Rule 462(b) under the Securities Act, please check the following 
box and list the Securities Act registration statement number of the earlier 
effective registration statement for the same offering. / /
     If this form is a post-effective amendment filed pursuant to Rule 462(c) 
under the Securities Act, check the following box and list the Securities Act 
registration statement number of the earlier effective registration statement 
for the same offering./ /
      If delivery of the prospectus is expected to be made pursuant to Rule 
434, please check the following box./ /

                           ------------------------
<PAGE>


                        CALCULATION OF REGISTRATION FEE

<TABLE>
<CAPTION>
- ----------------------------------------------------------------------------------------------------------------------------
- ----------------------------------------------------------------------------------------------------------------------------
    TITLE OF SECURITIES          AMOUNT TO BE         PROPOSED MAXIMUM         PROPOSED MAXIMUM AGGREGATE      AMOUNT OF
      TO BE REGISTERED            REGISTERED     OFFERING PRICE PER SHARE (1)       OFFERING PRICE (1)     REGISTRATION FEE
- ----------------------------------------------------------------------------------------------------------------------------
<S>                               <C>                    <C>                        <C>                       <C>      
Common Stock, $.001 par value      1,684,209               $7.5625                    $12,736,831               $3,758
- ----------------------------------------------------------------------------------------------------------------------------
- ----------------------------------------------------------------------------------------------------------------------------
</TABLE>

(1) Estimated solely for the purpose of calculating the amount of the
    registration fee based on the average of the high and low sales prices on 
    the Nasdaq National Market on April 1, 1998.

THE REGISTRANT HEREBY AMENDS THIS REGISTRATION STATEMENT ON SUCH DATE OR 
DATES AS MAY BE NECESSARY TO DELAY ITS EFFECTIVE DATE UNTIL THE REGISTRANT 
SHALL FILE A FURTHER AMENDMENT THAT SPECIFICALLY STATES THAT THIS 
REGISTRATION STATEMENT SHALL THEREAFTER BECOME EFFECTIVE IN ACCORDANCE WITH 
SECTION 8(A) OF THE SECURITIES ACT OF 1933 OR UNTIL THE REGISTRATION 
STATEMENT SHALL BECOME EFFECTIVE ON SUCH DATE AS THE COMMISSION, ACTING 
PURSUANT TO SAID SECTION 8(A), MAY DETERMINE.

- -------------------------------------------------------------------------------
- -------------------------------------------------------------------------------

                                       2.

<PAGE>
Information contained herein is subject to completion or amendment.  A 
registration statement relating to these securities has been filed with the 
Securities and Exchange Commission.  These securities may not be sold nor may 
offers to buy be accepted prior to the time the registration statement 
becomes effective.  This prospectus shall not constitute an offer to sell or 
the solicitation of an offer to buy nor shall there be any sale of these 
securities in any State in which such offer, solicitation or sale would be 
unlawful prior to registration or qualification under the securities laws of 
any such State.

<PAGE>

                         SUBJECT TO COMPLETION DATED APRIL 2, 1998


PROSPECTUS

                               1,684,209 SHARES

                          ONYX PHARMACEUTICALS, INC.

                                 COMMON STOCK

                              -------------------


     This Prospectus relates to 1,684,209 shares of Common Stock, $.001 par 
value (the "Common Stock") which are being offered and sold by certain 
stockholders (the "Selling Shareholders") of ONYX Pharmaceuticals, Inc. (the 
"Company" or "Onyx").  The Selling Shareholders, directly or through agents, 
broker-dealers or underwriters, may sell the Common Stock offered hereby from 
time to time on terms to be determined at the time of sale, in transactions 
on the Nasdaq National Market or in privately negotiated transactions.  The 
Selling Shareholders and any agents, broker-dealers or underwriters that 
participate in the distribution of the Common Stock may be deemed to be 
"underwriters" within the meaning of the Securities Act of 1933, as amended 
(the "Securities Act"), and any commission received by them and any profit on 
the resale of the Common Stock purchased by them may be deemed to be 
underwriting discounts or commissions under the Securities Act.  The Company 
will not receive any proceeds from the sale of shares by the Selling 
Shareholders.  See "Selling Shareholders" and "Plan of Distribution."

     The Common Stock of the Company is quoted on the Nasdaq National Market 
under the symbol "ONXX."  The last reported sales price of the Company's 
Common Stock on the Nasdaq National Market on April 1, 1998 was $7.50 
per share.

                              -------------------

 THIS OFFERING INVOLVES A HIGH DEGREE OF RISK.  SEE "RISK FACTORS" ON PAGE 3.

                              -------------------

         THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE
           SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES
           COMMISSION NOR HAS THE SECURITIES AND EXCHANGE COMMISSION
               OR ANY STATE SECURITIES COMMISSION PASSED UPON THE
                 ACCURACY OR ADEQUACY OF THIS PROSPECTUS.  ANY
                      REPRESENTATION TO THE CONTRARY IS A
                               CRIMINAL OFFENSE.


     No underwriting commissions or discounts will be paid by the Company in 
connection with this offering.  Estimated expenses payable by the Company in 
connection with this offering are $45,000.  The aggregate proceeds to the 
Selling Shareholders from the Common Stock will be the purchase price of the 
Common Stock sold less the aggregate agents' commissions and underwriters' 
discounts, if any.  See "Plan of Distribution."

     The Company has agreed to indemnify the Selling Shareholders, and the 
Selling Shareholders have agreed to indemnify the Company against certain 
liabilities, including liabilities under the Securities Act.

     April __, 1998

                                       1.
<PAGE>
                                       
                             AVAILABLE INFORMATION

     The Company is subject to the informational requirements of the 
Securities Exchange Act of 1934, as amended (the "Exchange Act"), and in 
accordance therewith, files annual and quarterly reports, proxy statements 
and other information with the Securities and Exchange Commission (the 
"Commission"). Such reports, proxy statements and other information may be 
inspected and copied at the Commission's Public Reference Section, 450 Fifth 
Street, N.W., Washington, D.C. 20549, as well as at the following regional 
offices of the Commission: the New York Regional Office, 7 World Trade 
Center, Suite 1300, New York, New York 10048; and the Chicago Regional 
Office, Citicorp Center, 500 West Madison Street, Suite 1400, Chicago, 
Illinois 60661.  Copies of such material can be obtained at prescribed rates 
from the Public Reference Section of the Commission at 450 Fifth Street, 
N.W., Washington, D.C. 20549.  The Common Stock of the Company is quoted on 
the Nasdaq National Market.  Reports and other information concerning the 
Company may be inspected at the National Association of Securities Dealers, 
Inc. at 1735 K Street, N.W. Washington, D.C. 20006.

     A registration statement on Form S-3 with respect to the Common Stock 
offered hereby (the "Registration Statement") has been filed with the 
Commission under the Act.  This Prospectus does not contain all of the 
information contained in such Registration Statement and the exhibits and 
schedules thereto, certain portions of which have been omitted pursuant to 
the rules and regulations of the Commission.  For further information with 
respect to the Company and the Common Stock offered hereby, reference is made 
to the Registration Statement and the exhibits and schedules thereto.  
Statements contained in this Prospectus regarding the contents of any 
contract or any other documents are not necessarily complete and, in each 
instance, reference is hereby made to the copy of such contract or document 
filed as an exhibit to the Registration Statement.  The Registration 
Statement, including exhibits thereto, may be inspected without charge at the 
Commission's principal office in Washington, D.C., and copies of all or any 
part thereof may be obtained from the Public Reference Section, the 
Commission, at 450 Fifth Street, N.W., Washington, D.C., 20549, upon payment 
of the prescribed fees.

     The Commission maintains a World Wide Web site that contains reports, 
proxy and information statements and other information filed electronically 
with the Commission.  The address of the site is http://www.sec.gov.
                                       
                INCORPORATION OF CERTAIN DOCUMENTS BY REFERENCE

     The following documents, filed or to be filed with the Commission under 
the Exchange Act are hereby incorporated by reference into this Prospectus:

     (i)   The Company's Annual Report on Form 10-K for the fiscal year ended 
           December 31, 1997;

     (ii)  The Company's Current Report on Form 8-K filed with the Commission
           on January 26, 1998; and

     (iii) The Description of Capital Stock contained in the Company's Form 
           SB-2 Registration Statement filed with the Commission on April 1, 
           1996.

     All documents filed by the Company pursuant to Sections 13(a), 13(c), 14 
or 15(d) of the Exchange Act after the date of this Prospectus and prior to 
the termination of the offering shall be deemed to be incorporated by 
reference herein and to be a part hereof from the date of filing of such 
documents.  Any statement contained in this Prospectus or in a document 
incorporated or deemed to be incorporated by reference herein shall be deemed 
to be modified or superseded for purposes of this Prospectus to the extent 
that a statement contained herein or in any subsequently filed document which 
also is or is deemed to be incorporated by reference herein modifies or 
supersedes such statement.  Any such statement so modified or superseded 
shall not be deemed, except as so modified or superseded, to constitute a 
part of this Prospectus.

     The Company will provide without charge to each person, including any 
beneficial owner, to whom this Prospectus is delivered, upon written or oral 
request of such person, a copy of any and all of the documents that have been 
incorporated by reference herein (not including exhibits to such documents 
unless such exhibits are specifically incorporated by reference herein or 
into such documents).  Such request may be directed to ONYX Pharmaceuticals, 
Inc., Attention: Treasurer, 3031 Research Drive, Richmond, CA  94806, 
telephone (510) 222-9700.

                                       2.

<PAGE>

                                   THE COMPANY

     The Company was incorporated in California in 1992 and reincorporated 
in Delaware in 1996.  The Company's executive offices are located at 
3031 Research Drive, Richmond, California  94806, and its telephone number is 
(510) 222-9700.

     If the Company splits or combines the outstanding shares of Common Stock 
or declares a dividend of shares of Common Stock on the outstanding shares of 
Common Stock, the shares of Common Stock registered under this Registration 
Statement shall be adjusted accordingly.
                                       
                                 RISK FACTORS

     THIS PROSPECTUS CONTAINS FORWARD-LOOKING STATEMENTS THAT INVOLVE RISKS 
AND UNCERTAINTIES.  ACTUAL RESULTS MAY DIFFER MATERIALLY FROM THOSE DISCUSSED 
IN THE FORWARD-LOOKING STATEMENTS THAT INVOLVE RISKS AND UNCERTAINTIES, 
INCLUDING THOSE SET FORTH BELOW.  PROSPECTIVE INVESTORS SHOULD CONSIDER THE 
FOLLOWING FACTORS IN EVALUATING THE COMPANY AND ITS BUSINESS BEFORE 
PURCHASING ANY SHARES OF THE COMMON STOCK OFFERED HEREBY.

UNCERTAINTIES RELATED TO EARLY STAGE OF DEVELOPMENT

     Onyx is at an early stage of development and must be evaluated in light 
of the uncertainties present in an early stage biotechnology company.  Since 
its inception in 1992, the Company has devoted substantially all of its 
resources to the research and development of potential products and no 
revenue has been generated from product sales.  If any products result from 
the Company's research and development programs, they are not expected to be 
commercially available for a number of years even if they are successfully 
developed and proven to be safe and effective.  There can be no assurance 
that any of the Company's product development efforts will be successfully 
completed, that any of the Company's products will be proven to be safe and 
effective, that regulatory approvals will be obtained at all or be as broad 
as sought, that the Company's products will be capable of being produced in 
commercial quantities at reasonable cost or that any products, if introduced, 
will achieve market acceptance.

TECHNOLOGICAL UNCERTAINTY

     Drug discovery methods based upon the genetic basis of cancer are 
relatively new, and there can be no assurance that the Company will be able 
to employ these methods of drug discovery successfully or that these methods 
will lead to the discovery of commercially viable pharmaceutical products.  
Only one of the Company's compounds, the Company's lead product, ONYX-015, a 
therapeutic virus ("ONYX-015"), has entered human clinical trials, and there 
can be no assurance that any of the Company's other current or future 
research and development programs will lead to additional compounds which 
will be submitted for clinical testing or advance to human clinical trials.  
Although the Company has demonstrated the safety of ONYX-O15 in human 
clinical trials, the Company has not demonstrated the efficacy of any of the 
Company's compounds, including ONYX-O15, in human clinical trials.  The 
effect of the human immune response on the ONYX-015 therapeutic virus cannot 
be predicted and could cause significant delays in the development process.  
The Company's ras and Cell Cycle Programs are also in the early stages of 
research and development, and the Company does not expect that its 
collaborative partners will commence clinical trials prior to the year 2000.  
The Company currently does not expect that clinical trials of any potential 
products arising from its BRCA1 or APC Programs will commence for at least 
several years.  Even if the Company's potential products are found to be safe 
or efficacious, or otherwise to have utility, they will require significant 
additional research and development efforts, preclinical and clinical 
testing, regulatory approvals, and additional investment prior to their 
commercialization, and there can be no assurance that any of these efforts 
will be successful.

UNCERTAINTIES RELATED TO CLINICAL TRIALS

     Before obtaining regulatory approvals for the commercial sale of any of 
its products under development, the Company or its collaborative partners 
must demonstrate through preclinical testing and clinical trials that the 
product is safe and effective for use in each target indication. The results 
from preclinical testing and early clinical trials may not be predictive of 
results that will be obtained in later clinical trials and large-scale 
testing, and there can be no assurance that clinical trials of products 
identified by or developed in collaboration with the Company will demonstrate 
sufficient safety and efficacy to obtain the requisite regulatory approvals 
or will result in marketable 

                                       3.

<PAGE>
products. Clinical trials may require the enrollment of large numbers of 
patients and suitable patients may be difficult to identify and recruit.  A 
number of companies in the pharmaceutical industry have suffered significant 
setbacks in every stage of clinical trials, even in advanced clinical trials 
after promising results in earlier trials. Any delays in, or termination of, 
the clinical trial efforts of the Company or its collaborative partners would 
have a material adverse effect on the Company's business, financial condition 
and results of operations.

UNCERTAINTIES REGARDING CLINICAL TRIALS OF ONYX-015

     The Company is currently engaged in three self-funded Phase II clinical 
trials of ONYX-015 for the treatment of head and neck cancer.  The ability of 
the Company to obtain a corporate partner for the p53 program and to continue 
to develop ONYX-015 as a potential product will depend materially on the 
results of these trials.  The Company expects to present the results of the 
first trial in the second quarter of 1998 and the results of the other trials 
later in the year.  There is no assurance that such results will be positive 
or, even if they are positive, that they will be sufficiently strong to 
support the Company's corporate partnering or product development objectives. 
In this regard, while the Phase I trials of ONYX-015 demonstrated a very 
favorable safety profile and, in many patients, tumor necrosis, the 
observation of viral replication was less pronounced than was the case in 
animal studies.  If the Phase II clinical trial results do not support the 
commencement of a Phase III pivotal trial, the Company would be required to 
conduct additional Phase I and Phase II clinical trials to determine an 
appropriate indication and treatment regimen for ONYX-015, if it were to 
continue development of such product.

NEED TO ATTRACT AND RETAIN KEY EMPLOYEES AND CONSULTANTS

     The Company is highly dependent on its corporate officers and other 
principal members of its scientific and management staff, the loss of any of 
whose services might significantly delay or prevent the achievement of the 
Company's research, development or business objectives. In addition, the 
Company relies on consultants and advisors, including the members of its 
Scientific Advisory Board, to assist the Company in formulating its research 
and development strategy. None of the Company's consultants and advisors are 
employees of the Company and all have commitments to, or consulting or 
advisory contracts with, other entities that may limit their availability to 
the Company.  In order to pursue its product development plans, the Company 
will be required to hire additional qualified scientific personnel to perform 
research and development, as well as personnel with expertise in clinical 
testing, government regulation and manufacturing. These requirements are also 
expected to demand additional management personnel and the development of 
additional expertise by existing management personnel. The Company faces 
competition for qualified individuals from numerous pharmaceutical and 
biotechnology companies, universities and other research institutions. There 
can be no assurance that the Company will be able to attract and retain such 
individuals on acceptable terms, if at all, and the failure to do so would 
have a material adverse effect on the Company, including its ability to enter 
into additional collaborative arrangements.

DEPENDENCE ON COLLABORATIVE AGREEMENTS

     The Company's strategy for the development, clinical trials, 
manufacturing and commercialization of its products includes maintaining and 
entering into various collaborations with corporate partners, licensors, 
licensees and others.  To date, the Company has entered into collaborative 
arrangements with Bayer Corporation with respect to the Company's ras 
Program, Warner-Lambert Company with respect to the Company's Cell Cycle 
Program and the Company's Inflammation Program, and Eli Lilly & Company with 
respect to the Company's BRCA1 Program.  The Company is currently seeking a 
collaborative partner for its p53 program, including the development and 
commercialization of ONYX-015. There can be no assurance that the Company 
will be able to maintain existing collaborative agreements, negotiate 
collaborative arrangements in the future on acceptable terms, if at all, or 
that any such collaborative arrangements will be successful. To the extent 
that the Company is not able to maintain or establish such arrangements, the 
Company would be required to undertake such activities at its own expense, 
which would significantly increase the Company's capital requirements and 
limit the programs the Company is able to pursue. In addition, the Company 
may encounter significant delays in introducing its products into certain 
markets or find that the development, manufacture or sale of its products in 
such markets is adversely affected by the absence of such collaborative 
agreements.
                                       4.
<PAGE>

     The Company cannot control the amount and timing of resources which its 
collaborative partners devote to the Company's programs or potential 
products, which can vary because of factors unrelated to the potential 
product. These relationships may in some cases be terminated at the 
discretion of the Company's collaborative partners with only limited notice 
to the Company and for reasons outside the Company's control. If any of the 
Company's collaborative partners breach or terminate their agreements with 
the Company or otherwise fail to conduct their collaborative activities in a 
timely manner, the preclinical or clinical development or commercialization 
of product candidates or research programs will be delayed, and the Company 
will be required to devote additional resources to product development and 
commercialization or terminate certain development programs. There also can 
be no assurance that disputes will not arise in the future with respect to 
the ownership of rights to any technology developed with third parties. These 
and other possible disagreements between collaborators and the Company could 
lead to delays in the collaborative research, development or 
commercialization of certain product candidates or could require or result in 
litigation or arbitration, which would be time consuming and expensive, and 
would have a material adverse effect on the Company's business, financial 
condition and results of operations.

     In addition, the Company's collaborative partners may develop, either 
alone or with others, products that compete with the development and 
marketing of the Company's products. Competing products, either developed by 
the collaborative partners or to which the collaborative partners have 
rights, may result in their withdrawal of support with respect to all or a 
portion of the Company's technology, which would have a material adverse 
effect on the Company's business, financial condition and results of 
operations.

UNCERTAINTY OF FUTURE PROFITABILITY; ACCUMULATED DEFICIT

     The Company has generated no revenues from product sales and has 
experienced significant operating losses since inception. As of December 31, 
1997, the Company had an accumulated deficit of approximately $45.6 million. 
The Company expects to incur significant and increasing operating losses over 
at least the next several years as the Company's research and development 
efforts and preclinical testing and clinical trial activities expand. The 
Company does not expect to generate revenues from the sale of its potential 
products, if any, for the foreseeable future. The Company's ability to 
achieve profitability depends in part upon its ability, alone or with others, 
to complete development of its potential products, to obtain required 
regulatory approvals and to successfully manufacture and market such 
potential products. The Company expects its operating expenses and operating 
losses to increase in 1998 and beyond. There can be no assurance that Onyx, 
or its collaborative partners, will successfully develop, manufacture, 
commercialize and market any potential product, or that the Company will ever 
achieve product revenues or profitability.

NEED FOR FUTURE FUNDING; UNCERTAINTY OF ACCESS TO CAPITAL

     The development of the Company's technology and proposed products will 
require a commitment of substantial funds to conduct the costly and 
time-consuming research and preclinical testing and clinical trials necessary 
to develop such technology and proposed products, and to establish 
relationships with collaborative partners to bring any such products to 
market. The Company's future capital requirements will depend upon a number 
of factors, including continued scientific progress in the research and 
development of the Company's technology programs, the size and complexity of 
these programs, the ability of the Company to establish and maintain 
collaborative arrangements, progress with preclinical testing and clinical 
trials, the time and costs involved in obtaining regulatory approvals, the 
cost involved in preparing, filing, prosecuting, maintaining and enforcing 
patent claims, competing technological and market developments and product 
commercialization activities.

     The Company believes that its existing capital resources and interest 
thereon, and anticipated revenues from existing collaborations will be 
sufficient to fund its current and planned operations through 1999.  There 
can be no assurance, however, that changes in the Company's research and 
development plans or other changes affecting the Company's operating expenses 
will not result in the expenditure of such resources before such time, and in 
any event, the Company will need to raise substantial additional capital to 
fund its operations in future periods.  The Company intends to seek such 
additional funding through collaborative arrangements, public or private 
equity or debt financings, capital lease transactions or other financing 
sources that may be available.  However, there can be no assurance that 
additional financing will be available on acceptable terms or at all.  If 
additional funds are raised by issuing equity securities, substantial 
dilution to existing stockholders may result.  If adequate funds are not 
available, the Company may be required to delay, reduce the scope of, or 
eliminate one or more of its research or 

                                       5.
<PAGE>

development programs or to obtain funds through collaborative arrangements 
with others that are on unfavorable terms or that may require the Company to 
relinquish rights to certain of its technologies, product candidates or 
products that the Company would otherwise seek to develop itself.

INTENSE COMPETITION AND RISK OF TECHNOLOGICAL OBSOLESCENCE

     Onyx is engaged in a rapidly changing and highly competitive field.  
Other products and therapies that will compete directly with the products 
that the Company is seeking to develop and market currently exist or are 
being developed.  Many other companies are actively seeking to develop 
products that have disease targets similar to those being pursued by the 
Company.  Some of these competitive products are in clinical trials.  There 
can be no assurance that the Company's competitors will not succeed in 
developing cancer-specific therapies that are more effective than any that 
are being developed or may be developed by the Company, or that would render 
the Company's technologies obsolete and noncompetitive.  Moreover, there are 
currently commercially available products for the treatment of certain 
disease targets being pursued by the Company.

     Competition from fully integrated pharmaceutical companies and more 
established biotechnology companies is intense and is expected to increase. 
Substantially all of these companies have significantly greater financial 
resources and expertise in research and development, manufacturing, 
preclinical and clinical testing, obtaining regulatory approvals, and 
marketing than the Company.  Smaller companies may also prove to be 
significant competitors, particularly through collaborative arrangements with 
large pharmaceutical and established biotechnology companies.  Many of these 
competitors have significant products that have been approved or are in 
development and operate large, well-funded research and development programs. 
Academic institutions, governmental agencies and other public and private 
research organizations also conduct research, seek patent protection and 
establish collaborative arrangements for products and clinical development 
and marketing that compete with the Company's programs.  These companies and 
institutions also compete with the Company in recruiting and retaining highly 
qualified scientific and management personnel.  In addition to the above 
factors, Onyx will face competition based on product efficacy and safety, the 
timing and scope of regulatory approvals, availability of supply, marketing 
and sales capability, reimbursement coverage, price and patent position.  
There is no assurance that the Company's competitors will not develop more 
effective or more affordable products, or achieve earlier patent protection 
or product commercialization than the Company.

UNCERTAINTY OF PROTECTION OF PATENTS AND PROPRIETARY RIGHTS; DEPENDENCE UPON 
TRADE SECRETS

     The Company believes that patent and trade secret protection is crucial 
to its business and that its future will depend in part on its ability to 
obtain patents, maintain trade secret protection and operate without 
infringing the proprietary rights of others, both in the United States and 
other countries. In October 1997, the Company was awarded a United States 
patent, No. 5,677,178 from the United States Patent and Trademark Office for 
claims covering the use of ONYX-015 for the treatment of p53-deficient 
cancers.  Additionally, the Company has received two notices of allowance for 
two United States patent applications, the first of which claims certain 
adenoviral mutants that kill Rb- tumor cells and another that claims 
compositions of matter that consist of ONYX-015 and a chemotherapeutic.  As 
of March 5, 1998, the Company owned or had licensed rights to 19 United 
States patents and 42 United States patent applications, and generally, 
foreign counterparts of these filings.  These patents and patent applications 
cover in most cases discoveries made with respect to biological materials and 
interactions of biological materials, including research tools used by the 
Company in its drug discovery programs. The Company's rights under five of 
the United States patents and nine of the United States patent applications 
are nonexclusive rights held under a license from Chiron Corporation that was 
granted to the Company in connection with its formation.  Additionally, the 
Company has exclusive rights to one patent application under the Chiron 
license.  The Company also has nonexclusive rights under one United States 
patent held under license from the State University of New York-Stony Brook.

     The Company's existing patent rights may not have a deterrent effect on 
competitors who are conducting or desiring to commence competitive research 
programs with respect to the biological targets or fields of inquiry being 
pursued by the Company.  The Company's ultimate patent position will depend 
on the success of its drug discovery program and its ability to obtain 
effective patent coverage for the compositions of matter identified in such 
drug discovery programs.  Because the Company's drug discovery programs are 
at an early stage and, except in the p53 

                                       6.
<PAGE>

Program, potential products have not yet been identified, it cannot be 
determined whether potential products that may be derived from the Company's 
drug discovery program may be subject to the patent rights of third parties.

     Since patent applications in the United States are maintained in secrecy 
until patents issue and since publication of discoveries in the scientific or 
patent literature often lag behind actual discoveries, the Company cannot be 
certain that it was the first to make the inventions covered by each of its 
pending patent applications or that it was the first to file patent 
applications for such inventions.  The patent positions of biotechnology and 
pharmaceutical companies are highly uncertain and involve complex legal and 
factual questions. Therefore, the breadth of claims allowed in biotechnology 
and  pharmaceutical patents, or their enforceability, cannot be predicted.  
To date there has emerged no consistent policy regarding the breadth of 
claims allowed in biotechnology patents.  There can be no assurance that any 
of the Company's patents or patent applications, if issued, will not be 
challenged, invalidated or circumvented, or that the rights granted 
thereunder will provide proprietary protection or competitive advantages to 
the Company against competitors with similar technology.  Furthermore, there 
can be no assurance that others will not independently develop similar 
technologies or duplicate any technology developed by the Company.  Because 
of the extensive time required for development, testing and regulatory review 
of a potential product, it is possible that before any of the Company's 
products can be commercialized, any related patent may expire, or remain in 
existence for only a short period following commercialization, thus reducing 
any advantage of the patent.

     The Company is aware of pending patent applications that have been filed 
by others that may pertain to certain aspects of the Company's programs.  If 
patents are issued to others containing preclusive or conflicting claims and 
such claims are ultimately determined to be valid, the Company may be 
required to obtain licenses to these patents or to develop or obtain 
alternative technology.  The Company's breach of an existing license or 
failure to obtain a license to technology required to commercialize its 
products may have a material adverse effect on the company's business,  
financial condition and results of operations.  Litigation, which could 
result in substantial costs to the Company, may also be necessary to enforce 
any patents issued to the Company or to determine the scope and validity of 
third-party proprietary rights.  If competitors of the Company prepare and 
file patent applications in the United States that claim technology also 
claimed by the Company, the Company may have to participate in interference 
proceedings declared by the United States Patent and Trademark Office to 
determine priority of invention, which could result in substantial cost to 
the Company, even if the eventual outcome is favorable to the Company.  An 
adverse outcome could subject the Company to significant liabilities to third 
parties and require the company to seek licenses of the disputed rights from 
third parties or to cease using such technology if such licenses are not 
available, and could have a material adverse effect on the Company's 
business, financial condition and results of operations.

     In respect of the foregoing, the Company is aware of a patent 
application filed in the United States, Europe, Japan and Canada by General 
Hospital Corporation, an affiliate of Massachusetts General Hospital.  This 
patent application is related to research involving a modified herpes simplex 
virus but it also includes broader claims that, if they were to issue, would 
cover the p53 Program including ONYX-015.  The Company believes, and has 
received an opinion from outside counsel to the effect, that claims made in 
the General Hospital patent application that may infringe on ONYX-015 and the 
p53 Program are not patentable.  However, there can be no assurance that 
broad claims applicable to ONYX-015 or the p53 Program will not issue from 
the General Hospital patent application in one or more countries, that the 
Company would be successful in challenging any such claims, or that a license 
would be available under any such patent if it were to issue.

     In June 1997, ICT Pharmaceuticals, Inc. ("ICT") notified the Company of 
two issued United States Patents, Nos. 4,980,281 and 5,266,464 that ICT 
believes cover the use of a cell for the screening, testing or 
pharmacological characterization of new drugs or other substances.  Foreign 
counterparts of the United States Patents are pending.  ICT has offered the 
Company a license to the patents.  The Company has not determined whether to 
negotiate a license. In any event, the Company does not believe that these 
patents will have a material adverse effect on the Company's business, 
assets, liabilities, financial condition, operations or prospects.

     The Company has identified two issued United States Patents, Nos. 
5,499,755 and 5,645,999 that cover recombinant cyclin E compositions, or 
methods of using the same to identify possible drug candidates, respectively. 
Foreign counterparts of the United States Patents are pending.  Mitotix 
Corporation ("Mitotix") either owns, or has licensed the rights to the two 
patents.  The Company may seek a license under the patents from Mitotix.  If 
such 

                                       7.
<PAGE>

license is not  available at commercially reasonable terms, or at all, then 
the Company would be required to develop assays that are not covered by the 
patents.  In any event, the Company does not believe that these patents will 
have a material adverse effect on the Company's business, assets, 
liabilities, financial condition, operations or prospects.

     The Company has also identified an additional issued United States 
Patent, No. 5,691,147, that covers an assay for screening test compounds for 
an inhibitor of an interaction of a cyclin-dependant kinase with a 
cyclin-dependent kinase 4 binding protein.  Mitotix either owns or has 
licensed the rights to the patent.  A foreign counterpart of the United 
States Patent is pending.  The Company may seek a license under the patent 
from Mitotix.  If such license is not available on commercially reasonable 
terms, or at all, then the Company would be required to develop assays that 
are not covered by the patent.

     The Company has further identified three issued United States Patents, 
Nos. 5,441,880, 5,695,950 and 5,443,962 that cover assays and compositions 
for identifying inhibitors of CDC25, respectively.  Foreign counterparts of 
the United States Patents are pending.  Mitotix either owns, or has licensed 
the rights to these patents.  The Company has approached Mitotix for a 
license and the request was denied.  Consequently, should the Company wish to 
use the methods and compositions covered in these patents to identify 
inhibitors of CDC25, it will have to do so abroad, while the foreign 
applications are still pending and before they are granted.  Alternatively, 
the Company may be required to develop methods and compositions that are not 
covered by these patents if it wishes to identify inhibitors of CDC25.

     The Company and its licensors also rely on trade secrets to protect 
their technology, especially where patent protection is not believed to be 
appropriate or obtainable.  However, trade secrets are difficult to protect. 
The Company protects its proprietary technology and processes, in part, by 
confidentiality agreements with its employees, consultants, collaborative 
partners and certain contractors.  There can be no assurance that these 
agreements will not be breached, that the Company would have adequate 
remedies for any breach, or that the Company's trade secrets will not 
otherwise become known or be independently discovered by competitors.  To the 
extent that Onyx or its consultants, or research collaborators use 
intellectual property owned by others in their work for the Company, disputes 
may also arise as to the rights in related or resulting know-how and 
inventions.

SIGNIFICANT GOVERNMENT REGULATION; NO ASSURANCE OF REGULATORY APPROVALS

     The Company's ongoing research and development activities and, if any 
product is successfully developed and obtains regulatory approval, the 
production and marketing of the Company's products are subject to extensive 
regulation by numerous government authorities in the United States and other 
countries. Prior to marketing in the United States, any product developed by 
the Company must undergo rigorous preclinical testing and clinical trials and 
an extensive regulatory approval process implemented by the Food and Drug 
Administration (the "FDA") under the Food, Drug and Cosmetic Act and the 
United States Public Health Service Act.  Satisfaction of such regulatory 
requirements, which includes demonstrating that the product is both safe and 
effective, typically takes several years or more depending upon the type, 
complexity and novelty of the product and requires the expenditure of 
substantial resources. Because certain of the products that may result from 
the Company's research and development programs involve the application of 
new technologies and will be based on new therapeutic approaches, such 
products may be subject to substantial additional review by various 
governmental regulatory authorities and as a result, regulatory approvals may 
be obtained more slowly than for products using more conventional 
technologies.  There can be no assurance that FDA and other regulatory 
approvals will be obtained in a timely manner, or at all. Any delay in 
obtaining, or the failure to obtain, such approvals would adversely affect 
the Company's ability to generate product or royalty revenues. Preclinical 
studies to demonstrate product safety must be conducted in conformance with 
the FDA's Good Laboratory Practice regulations. Clinical testing must meet 
requirements for institutional review board oversight and informed consent, 
as well as FDA prior review, oversight and Good Clinical Practice 
requirements.  The Company or the FDA may suspend clinical trials at any time 
if it believes that the subjects participating in such trials are being 
exposed to unacceptable health risks. Even if FDA and other regulatory 
approvals are obtained, the marketing and manufacturing of products are 
subject to continuing FDA and other regulatory review, and later discovery of 
previously unknown problems with a product, manufacturer or facility may 
result in restrictions on the product or manufacturer, including withdrawal 
of the product from the market. Additional governmental regulations may be 
promulgated that could delay regulatory approval of the Company's or a 
corporate partner's potential products. The Company cannot predict the impact 
of adverse governmental regulation which might arise from future legislative 
or administrative action.

                                       8.
<PAGE>

     Accordingly, no assurance can be given that the Company will ever 
receive approval from the FDA or foreign regulatory authorities for any of 
its products and the failure to receive such approval, or significant delays 
in obtaining such approval, could prevent the commercial development of such 
products and would have a material adverse effect on the Company.

LACK OF MANUFACTURING EXPERIENCE

     The Company's collaborative partners generally have the exclusive right 
to manufacture products resulting from the collaborations, and the Company 
expects to have similar manufacturing arrangements in its other 
collaborations. The Company currently does not have the facilities to 
manufacture products for small or large-scale clinical trials or in 
commercial quantities, and has no experience in such manufacturing. The 
Company is dependent on third parties, including its collaborative partners, 
for the manufacturing of its products. There can be no assurance that such 
parties will be able to meet the Company's needs either with respect to 
timing, quantity or quality. If the Company is unable to obtain or retain 
third-party manufacturing on acceptable terms, it may be delayed in its 
ability to commercialize products. The Company's dependence upon third 
parties, including its collaborative partners, for the manufacturing of 
products may adversely affect the Company's profit margins and its ability to 
develop, deliver and sell products on a timely and competitive basis. In the 
event the Company undertakes to establish its own commercial manufacturing 
capabilities, it will require substantial additional funds, manufacturing 
facilities, equipment and personnel.

UNCERTAINTY OF MARKET ACCEPTANCE

     Even if the requisite regulatory approvals are obtained for the 
Company's potential products or for products developed in collaboration with 
the Company, uncertainty exists as to whether such products will be accepted 
by the market. A number of additional factors also may limit the market 
acceptance of products which may be developed by or discovered through 
collaboration with the Company, including the rate of adoption by health care 
practitioners, the indications for which the product is approved, the rate of 
the products' acceptance by the target population, the timing of market entry 
relative to competitive products, the availability of alternative therapies, 
the price of the Company's product relative to alternative therapies, the 
availability of third-party reimbursement and the extent of marketing efforts 
by the Company and third-party distributors or agents retained by the 
Company. Side effects or unfavorable publicity concerning the Company's 
products or any similar product could have an adverse effect on the Company's 
ability to obtain physician, patient or third-party payor acceptance and on 
efforts to sell the Company's products. There can be no assurance of the 
Company's ability, or the length of time required, to achieve 
commercialization of the Company's products or that physicians, patients or 
third-party payors will accept any of the Company's products as readily as 
alternative therapies or at all.

LACK OF MARKETING EXPERIENCE; DEPENDENCE ON THIRD PARTIES

     The Company currently has no sales, marketing or distribution 
capability. The Company intends to rely on relationships with one or more 
pharmaceutical companies with established distribution systems and direct 
sales forces to market its products. In the event that the Company is unable 
to reach agreement with one or more pharmaceutical companies to market its 
products, it may be required to market its products directly and to develop a 
marketing and sales force with technical expertise and supporting 
distribution capability. There can be no assurance that the Company will be 
able to establish in-house sales and distribution capabilities or 
relationships with third parties, or that it will be successful in gaining 
market acceptance for its products. To the extent that the Company enters 
into co-promotion or other licensing arrangements, the Company must develop 
its own sales, marketing or distribution capability, and there can be no 
assurance that such efforts will be successful.

RISK OF PRODUCT LIABILITY; UNCERTAINTY OF AVAILABILITY OF INSURANCE

     The Company's business will expose it to potential product liability 
risks that are inherent in the testing, manufacturing and marketing of human 
therapeutic products. The Company has obtained clinical trial liability 
insurance but there can be no assurance that it will be able to maintain such 
insurance for any of its clinical trials. In addition, there can be no 
assurance that the Company will be able to obtain or maintain product 
liability insurance in the future on acceptable terms or with adequate 
coverage against potential liabilities.

                                       9.
<PAGE>

UNCERTAINTY RELATED TO PHARMACEUTICAL PRICING AND REIMBURSEMENT

     In both domestic and foreign markets, sales of the Company's proposed 
products will depend in part upon the availability of reimbursement from 
third-party payors, such as government health administration authorities, 
private health insurers and other organizations. In addition, other 
third-party payors are increasingly challenging the price and cost 
effectiveness of medical products and services. Significant uncertainty 
exists as to the reimbursement status of newly approved health care products. 
There can be no assurance that the Company's potential products or products 
discovered in collaboration with the Company will be considered 
cost-effective or that adequate third-party reimbursement will be available 
to enable Onyx to maintain price levels sufficient to realize an appropriate 
return on its investment in product research, discovery and development. 
Legislation and regulations affecting the pricing of pharmaceuticals may 
change before the Company's proposed products are approved for marketing. 
Adoption of such  legislation could further limit reimbursement for medical 
products. If adequate coverage and reimbursement levels are not provided by 
the government and third-party payors for the Company's products, the market 
acceptance of these products would be adversely affected, which would have a 
material adverse effect on the Company's business, financial condition and 
results of operations.

RISKS ASSOCIATED WITH HAZARDOUS MATERIALS

     The Company's research and development involves the controlled use of 
hazardous materials, chemicals and various radioactive compounds. Although 
the Company believes that its safety procedures for handling and disposing of 
such materials comply with the standards prescribed by state and federal 
regulations, the risk of accidental contamination or injury from these 
materials cannot be completely eliminated. In the event of such an accident, 
the Company could be held liable for any damages that result and any such 
liability could exceed the resources of the Company. The Company may incur 
substantial costs to comply with environmental regulations if the Company 
develops manufacturing capacity.

VOLATILITY OF COMMON STOCK PRICE

     The market prices for securities of pharmaceutical and biotechnology 
companies, including Onyx, have historically been highly volatile. The market 
has from time to time experienced significant price and volume fluctuations 
that are unrelated to the operating performance of particular companies. In 
addition, factors such as fluctuations in the Company's operating results, 
future sales of Common Stock, announcements of technological innovations or 
new therapeutic products by the Company or its competitors, announcements of 
collaborative partners, clinical trial results, government regulation, 
developments in patent or other proprietary rights, public concern as to the 
safety of drugs developed by the Company or others, comments made, including 
changes in recommendations, by securities analysts, and general market 
conditions can have a significant adverse effect on the market price of the 
Common Stock. In particular, the realization of any of the risks described in 
these "Risk Factors" could have a significant adverse impact on such market 
price.

CONTROL BY EXISTING STOCKHOLDERS

     Executive officers and directors of the Company and other holders of 5% 
or more of the capital stock of the Company, together with entities 
affiliated with them, beneficially own approximately 45% of the Common Stock 
of the Company. Bayer Corporation has the right to have its nominee elected 
to the Company's Board of Directors until the later of (i) the end of the 
research term or (ii) if the parties have a Collaboration Compound (as 
defined in the collaboration agreements) in clinical development, until such 
time as the parties do not have a Collaboration Compound in clinical 
development. In addition, International Biotechnology Trust plc has the right 
to have its nominee elected to the Company's Board of Directors as long as it 
continues to own more than 66 2/3% of the Common Stock purchased by it from 
the Company on January 12, 1998.  Because of such ownership and voting 
arrangements, these officers, directors and stockholders may be able to 
effectively control the election of all members of the Board of Directors and 
to determine all corporate actions.

                                       10.
<PAGE>

ANTI-TAKEOVER EFFECTS OF DELAWARE LAW AND CERTAIN CHARTER PROVISIONS

     The Company's Board of Directors has the authority to issue up to 
5,000,000 shares of preferred stock and to determine the price, rights, 
preferences and privileges of those shares without any further vote or action 
by the Company's stockholders. The rights of the holders of Common Stock will 
be subject to, and may be adversely affected by, the rights of the holders of 
any preferred stock that may be issued in the future. While the Company has 
no present intention to issue shares of preferred stock, such issuance, while 
providing desirable flexibility in connection with possible acquisitions and 
other corporate purposes, could have the effect of making it more difficult 
for a third party to acquire a majority of the outstanding voting stock of 
the Company. In addition, the Company is subject to the anti-takeover 
provisions of Section 203 of the Delaware General Corporation Law, which 
prohibits the Company from engaging in a "business combination" with an 
"interested stockholder" for a period of three years after the date of the 
transaction in which the person became an interested stockholder, unless the 
business combination is approved in a prescribed manner.  The application of 
Section 203 could have the effect of delaying or preventing a change of 
control of the Company. The Company's Certificate of Incorporation provides 
for staggered terms for the members of the Board of Directors. The staggered 
Board of Directors and certain other provisions of the Company's Certificate 
of Incorporation and Bylaws may have the effect of delaying or preventing 
changes in control or management of the Company, which could adversely affect 
the market price of the Company's common stock.

ADDITIONAL FINANCINGS

     Future sales of substantial amounts of Common Stock in the public market 
could have an adverse effect on the price of Common Stock.  Such sales might 
also impair the Company's ability to raise additional funds through equity 
financing.  In such event, to the extent that funds generated from 
operations, together with the Company's existing capital resources, are 
insufficient to meet the Company's capital requirements, the Company will be 
required to rely on alternative sources of funding, including debt financing, 
corporate partnering arrangements and capital lease transactions.  No 
assurance can be given that additional financing will be available or, if 
available, will be available on acceptable terms.
                                       
                                USE OF PROCEEDS

     The Company will not receive any proceeds from the sale of Common Stock 
by the Selling Shareholders in the offering.

                                       11.
<PAGE>

                             SELLING SHAREHOLDERS

     The following table sets forth the names of the Selling Shareholders, 
the number of shares of Common Stock owned beneficially by each of them as of 
March 18, 1998 and the number of shares which may be offered pursuant to this 
Prospectus.  This information is based upon information provided by the 
Selling Shareholders. The Selling Shareholders may offer all, some or none of 
their Common Stock.

<TABLE>
<CAPTION>
                                                                                                         SHARES BENEFICIALLY
                                                       SHARES BENEFICIALLY              NUMBER OF              OWNED
                                                    OWNED PRIOR TO OFFERING(1)           SHARES          AFTER OFFERING(1)(2)
         NAME                                  NUMBER OF SHARES      PERCENT(3)       BEING OFFERED      NUMBER      PERCENT(3)
         ----                                  ----------------      ----------       -------------      ------      ----------
<S>                                            <C>                     <C>           <C>                <C>         <C> 
International Biotechnology 
Trust, plc ..............................              1,122,807        9.97%            1,122,807         0            *
Lombard Odier & Cie......................                561,402        4.98%              561,402         0            *
                                                                                         ---------
                                                                                         1,684,209
</TABLE>

- ----------------------
 *   Less than 1%

(1)  Unless otherwise indicated below, the persons named in the table have sole
     voting and investment power with respect to all shares beneficially owned
     by them, subject to community property laws where applicable.

(2)  Assumes the sale of all shares offered hereby.

(3)  Applicable percentage of ownership is based on 11,262,569 shares of Common
     Stock outstanding on March 18, 1998.

                                       12.
<PAGE>

                             PLAN OF DISTRIBUTION

     The shares of Common Stock offered by the Selling Shareholders may be 
sold from time to time to purchasers directly by any of the Selling 
Shareholders acting as principal for its own account in one or more 
transactions at a fixed price, which may be changed, or at varying prices 
determined at the time of sale or at negotiated prices.  Alternatively, any 
of the Selling Shareholders may from time to time offer the Common Stock 
through underwriters, dealers or agents who may receive compensation in the 
form of underwriting discounts, commissions or concessions from the Selling 
Shareholders and/or the purchasers of shares for whom they may act as agent.  
Sales may be made on the Nasdaq National Market or in private transactions.  
In addition to sales of Common Stock pursuant to the Registration Statement 
of which this Prospectus is a part, the Selling Shareholders may sell such 
Common Stock in compliance with Rule 144 promulgated under the Act.

     The Selling Shareholders and any agents, broker-dealers or underwriters 
that participate in the distribution of the Common Stock offered hereby may 
be deemed to be underwriters within the meaning of the Act, and any 
discounts, commissions or concessions received by them and any profit on the 
resale of the Common Stock purchased by them might be deemed to be 
underwriting discounts and commissions under the Act.

     In order to comply with the securities laws of certain states, if 
applicable, the Common Stock may be sold in such jurisdictions only through 
registered or licensed brokers or dealers.  In addition, in certain states 
the Common Stock may not be sold unless it has been registered or qualified 
for sale or an exemption from registration or qualification requirements is 
available and is complied with.

     Pursuant to the Stock Purchase Agreement dated January 12, 1998,  and 
the Stock Transfer Agreement dated January 12, 1998, the Company has agreed 
to register the Selling Shareholders' Common Stock under applicable federal 
and state securities laws under certain circumstances and at certain times.  
The Company will pay substantially all of the expenses incident to the 
offering and sale of the Common Stock to the public, other than commissions, 
concessions and discounts of underwriters, dealers or agents.  Such expenses 
(excluding such commissions and discounts) are estimated to be $45,000.  The 
above-referenced agreements provide for cross-indemnification of the Selling 
Shareholders and the Company to the extent permitted by law, for losses, 
claims, damages, liabilities and expenses arising, under certain 
circumstances, out of any registration of the Common Stock.

                                       
                                 LEGAL MATTERS

     The validity of the issuance of the Common Stock offered hereby will be 
passed upon for the Company by Cooley Godward LLP, Palo Alto, California.
                                       
                                    EXPERTS

     The financial statements of the Company appearing in the Company's 
Annual Report on Form 10-K for the year ended December 31, 1997, have been 
audited by Ernst & Young LLP, independent auditors, as set forth in their 
report thereon included therein, and incorporated herein by reference.  Such 
financial statements are incorporated herein by reference in reliance upon 
such report given upon the authority of such firm as experts in accounting 
and auditing.

                                       13.
<PAGE>

     No dealer, salesman or other person has been authorized to give any 
information or to make any representations other than those contained in this 
Prospectus and, if given or made, such other information and representations 
must not be relied upon as having been authorized by the Company.  This 
Prospectus does not constitute an offer or solicitation by anyone in any 
state in which such offer or solicitation is not authorized, or in which the 
person making such offer or solicitation is not qualified to do so, or to any 
person to whom it is unlawful to make such offer or solicitation.  The 
delivery of this Prospectus at any time does not imply that the information 
herein is correct as of any time subsequent to the date hereof.

                          ----------------------------
                                       
                               TABLE OF CONTENTS

<TABLE>
                                                             Page
<S>                                                          <C>
Available Information......................................     2
Incorporation of Certain
   Documents by Reference..................................     2
The Company................................................     3
Risk Factors...............................................     3
Use of Proceeds............................................    11
Selling Shareholders.......................................    12
Plan of Distribution.......................................    13
Legal Matters..............................................    13
Experts....................................................    13

</TABLE>

                          ----------------------------

                                       14.
<PAGE>

                                    PART II

                    INFORMATION NOT REQUIRED IN PROSPECTUS

ITEM 14.  OTHER EXPENSES OF ISSUANCE AND DISTRIBUTION

     The following table sets forth all expenses, other than the underwriting 
discounts and commissions, payable by ONYX Pharmaceuticals, Inc. (the 
"Registrant") in connection with the sale of the Common Stock being 
registered.  All the amounts shown are estimates except for the registration 
fee.

<TABLE>
<S>                                                         <C>
      Registration fee................................       $   3,758
      Printing and engraving expenses.................           2,000
      Legal fees and expenses.........................          10,000
      Accounting fees and expenses....................           3,000
      Nasdaq fee......................................          17,500
      Miscellaneous...................................           8,742
                                                             ---------
            Total.....................................       $  45,000
                                                             ---------
                                                             ---------
</TABLE>

ITEM 15.  INDEMNIFICATION OF OFFICERS AND DIRECTORS

     Under Section 145 of the Delaware General Corporation Law, the 
Registrant has broad powers to indemnify its directors and officers against 
liabilities they may incur in such capacities, including liabilities under 
the Securities Act of 1933.  The Registrant's Bylaws also provide that the 
Registrant will indemnify its directors and executive officers and may 
indemnify its other officers, employees and agents to the fullest extent 
permitted by Delaware Law.

     The Registrant's Certificate of Incorporation provides for the 
elimination of liability for monetary damages for breach of the directors' 
fiduciary duty of care to the Registrant and its stockholders.  These 
provisions do not eliminate the directors' duty of care and, in appropriate 
circumstances, equitable remedies such as injunctive or other forms of 
non-monetary relief will remain available under Delaware law.  In addition, 
each director will continue to be subject to liability for breach of the 
director's duty of loyalty to the Registrant, for acts or omissions not in 
good faith or involving intentional misconduct, for knowing violations of 
law, for any transaction from which the director derived an improper personal 
benefit, and for payment of dividends or approval of stock repurchases or 
redemptions that are unlawful under Delaware law.  The provision does not 
affect a director's responsibilities under any other laws, such as the 
federal securities laws or state or federal environmental laws.


                                      II-1
<PAGE>

ITEM 16.       EXHIBITS

     (a)  Exhibits.

<TABLE>
<CAPTION>
     EXHIBIT
     NUMBER         DESCRIPTION OF DOCUMENT
     ------         -----------------------
<S>           <C>
     4.6+      Stock Purchase Agreement, dated January 12, 1998, among the 
               Registrant, International Biotechnology Trust plc, and Lombard 
               Odier & Cie.
     4.7       Stock Transfer Agreement dated January 12, 1998, among the 
               Registrant, Chiron Corporation and Lombard Odier & Cie.
     5.1       Opinion of Cooley Godward LLP.
    23.1       Consent of Ernst & Young LLP, Independent Auditors.  Reference 
               is made to page II-6.
    23.2       Consent of Cooley Godward LLP.  Reference is made
               to Exhibit 5.1.
    24.1       Power of Attorney.  Reference is made to page II-4.
</TABLE>

+Filed as an exhibit to the Registrant's Current Report on Form 8-K
          filed on January 26, 1998 and incorporated herein by
          reference.

ITEM 17.  UNDERTAKINGS

     (a)  Rule 415 Offering

     The undersigned Registrant hereby undertakes:

     (1)  To file, during any period in which offers or sales are being made, 
a post-effective amendment to this registration statement to include any 
material information with respect to the plan of distribution not previously 
disclosed in the registration statement or any material change to such 
information in the registration statement;

     (2)  That, for the purpose of determining any liability under the 
Securities Act, each post-effective amendment that contains a form of 
prospectus shall be deemed to be a new registration statement relating to the 
securities offered therein, and the offering of such securities at that time 
shall be deemed to be the initial bona fide offering thereof; and

     (3)  To remove from registration by means of a post-effective amendment 
any of the securities being registered which remain unsold at the termination 
of the offering.

     The undersigned Registrant hereby undertakes that, for purposes of 
determining any liability under the Securities Act, each filing of the 
registrant's annual report pursuant to Section 13(a) or 15(d) of the Exchange 
Act that is incorporated by reference in the registration statement shall be 
deemed to be a new registration statement relating to the securities offered 
therein, and the offering of such securities at that time shall be deemed to 
be the initial BONA FIDE offering thereof.

     (b)  Acceleration of Effectiveness

     Insofar as indemnification for liabilities arising under the Securities 
Act may be permitted to directors, officers and controlling persons of the 
registrant pursuant to provisions described in Item 15, or otherwise, the 
registrant has been advised that in the opinion of the Commission such 
indemnification is against public policy as expressed in the Securities Act 
and is, therefore, unenforceable.  In the event that a claim for 
indemnification against such liabilities (other than the payment by the 
registrant of expenses incurred or paid by a director, officer or controlling 
person of the registrant in the successful defense of any action, suit or 
proceeding) is asserted by such director, officer or controlling person in 
connection with the securities being registered, the registrant will, unless 
in the opinion of its counsel the matter has been settled by controlling 
precedent, submit to a court of appropriate jurisdiction the question whether 
such indemnification by it is against public policy as expressed in the 
Securities Act and will be governed by the final adjudication of such issue.

     The undersigned Registrant hereby undertakes that, for purposes of 
determining any liability under the Securities Act, each filing of the 
Registrant's annual report pursuant to Section 13(a) or Section 15(d) of the 
Exchange Act (and, where applicable, each filing of an employee benefit 
plan's annual report pursuant to Section 15(d) of the Exchange Act) that is 
incorporated by reference in the Registration Statement shall be deemed to be 
a new registration statement relating to the securities offered therein, and 
the offering of such securities at that time shall be deemed to be the 
initial bona fide offering thereof.

     The undersigned Registrant hereby undertakes to deliver or cause to be 
delivered with the Prospectus, to each person to whom the Prospectus is sent 
or given, the latest annual report to security holders that is incorporated 
by reference in the Prospectus and furnished pursuant to and meeting the

                                     II-2
<PAGE>

requirements of Rule 14a-3 or Rule 14c-3 under the Exchange Act; and, where 
interim financial information required to be presented by Article 3 or 
Regulation S-X are not set forth in the Prospectus, to deliver, or cause to 
be delivered to each person to whom the Prospectus is sent or given, the 
latest quarterly report that is specifically incorporated by reference in the 
Prospectus to provide such interim financial information.

     (c)  Registration Statement Permitted by Rule 430A

     The undersigned Registrant hereby undertakes that:

          (1)  For purposes of determining any liability under the Securities 
Act, the information omitted from the form of prospectus filed as part of 
this Registration Statement in reliance upon Rule 430A and contained in a 
form of prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) 
or 497(h) under the Securities Act shall be deemed to be part of this 
Registration Statement as of the time it was declared effective.

          (2)  For the purpose of determining any liability under the 
Securities Act, each post-effective amendment that contains a form of 
prospectus shall be deemed to be a new registration statement relating to the 
securities offered therein, and the offering of such securities at that time 
shall be deemed to be the initial bona fide offering thereof.

                                      II-3
<PAGE>

                                       
                                  SIGNATURES


     Pursuant to the requirements of the Securities Act of 1933, as amended, 
the Registrant duly certifies that it has reasonable grounds to believe that 
it meets all of the requirements for filing on Form S-3 and has duly caused 
this Registration Statement to be signed on its behalf by the undersigned, 
thereunto duly authorized, in the City of Richmond, County of Contra Costa, 
State of California, on March 30, 1998.

                                   ONYX PHARMACEUTICALS, INC.



                                   By:   /s/ Hollings C. Renton
                                      ----------------------------------------
                                      Hollings C. Renton
                                      President and Chief Executive Officer

                                       
                               POWER OF ATTORNEY

     KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature 
appears below constitutes and appoints Hollings C. Renton and Douglas L. 
Blankenship and each or any one of them, as his true and lawful 
attorney-in-fact and agents with full power of substitution and 
resubstitution, for him and in his name, place and stead, in any and all 
capacities, to sign any and all amendments (including post-effective 
amendments) to this Registration Statement, and to file the same, with all 
exhibits thereto, and other documents in connection therewith, with the 
Securities and Exchange Commission, granting unto said attorneys-in-fact and 
agents, and each of them, full power and authority to do and perform each and 
every act and thing requisite and necessary to be done in connection 
therewith, as fully to all intents and purposes as he might or could do in 
person, hereby ratifying and confirming all that said attorneys-in-fact and 
agents, or any of them, or their or his substitutes or substitute, may 
lawfully do or cause to be done by virtue hereof.

     Pursuant to the requirements of the Securities Act of 1933, as amended, 
this Registration Statement has been signed below by the following persons in 
the capacities and on the dates indicated.

<TABLE>
<CAPTION>
  SIGNATURE                  TITLE                                 DATE
<S>                        <C>                                    <C>
                            
/s/ Hollings C. Renton      President, Chief Executive             March 30, 1998                        
- --------------------------  Officer and Director (PRINCIPAL                       
 Hollings C. Renton         EXECUTIVE OFFICER)             
                            
                            
                                                                        

/s/ Douglas L. Blankenship  Treasurer (PRINCIPAL FINANCIAL         March 30, 1998  
- --------------------------  AND ACCOUNTING OFFICER)                                
 Douglas L. Blankenship     
                            
                                                                   
/s/ Michael J. Berendt      Director                               March 31, 1998
- -------------------------   
 Michael J. Berendt         
                                                                         

/s/ Samuel D. Colella       Director                               March 30, 1998
- --------------------------  
 Samuel D. Colella          
                            

                                      II-4
<PAGE>

/s/ Paul Goddard            Director                               March 30, 1998
- -------------------------
 Paul Goddard               

                                                       
/s/ Kathleen LaPorte        Director                               March 30, 1998
- -------------------------
 Kathleen LaPorte           
                                                                      

/s/ Edward E. Penhoet       Director                               March 30, 1998
- -------------------------
 Edward E. Penhoet          
                                                                         

/s/ Ralph H. Thurman        Director                               March 30, 1998
- -------------------------
 Ralph H. Thurman           
                                                                         

/s/ Nicole Vitullo          Director                               March 30, 1998
- -------------------------
 Nicole Vitullo             
                                                                         

/s/ Wendell Wierenga        Director                               March 30, 1998
- -------------------------
 Wendell Wierenga           
                                                                         
</TABLE>

                                      II-5
<PAGE>

                                                                  EXHIBIT 23.1


               CONSENT OF ERNST & YOUNG LLP, INDEPENDENT AUDITORS


     We consent to the reference to our Firm under the caption "Experts" in 
the Registration Statement (Form S-3) and related Prospectus of ONYX 
Pharmaceuticals, Inc. for the registration of 1,684,209 shares of its common 
stock and to the incorporation by reference therein of our report dated 
February 20, 1998, with respect to the financial statements of ONYX 
Pharmaceuticals, Inc. included in its Annual Report (Form 10-K) for the year 
ended December 31, 1997, filed with the Securities and Exchange Commission.

                                                             Ernst & Young LLP


Palo Alto, California
March 30, 1998


                                      II-6
<PAGE>
                                       
                               INDEX TO EXHIBITS

<TABLE>
<CAPTION>
          SEQUENTIALLY
EXHIBIT   NUMBERED
NUMBER    DESCRIPTION OF DOCUMENT                                                        PAGE NUMBER
- ------    -----------------------                                                        -----------
<S>      <C>                                                                            <C>
4.6+      Stock Purchase Agreement, dated January 12, 1998, among the Registrant,
          International Biotechnology Trust plc and Lombard Odier & Cie

4.7       Stock Transfer Agreement, dated January 12, 1998, among the Registrant,
          Chiron Corporation and Lombard Odier & Cie

5.1       Opinion of Cooley Godward LLP

23.1      Consent of Ernst & Young LLP, Independent Auditors.  Reference 
          is made to page II-6

23.2      Consent of Cooley Godward LLP.  Reference is made to Exhibit 5.1.

24.1      Power of Attorney.  Reference is made to page II-4
</TABLE>

+Filed as an exhibit to the Registrant's Current Report on Form 8-K filed on
          January 26, 1998 and incorporated by reference herein.

                                      II-7

<PAGE>
                                       
                           STOCK TRANSFER AGREEMENT

     THIS STOCK TRANSFER AGREEMENT is entered into as of January 12, 1998, by 
and between LOMBARD ODIER & CIE (the "PURCHASER"), CHIRON CORPORATION 
("CHIRON") and, in regards to Section 3 only, ONYX PHARMACEUTICALS, INC. (the 
"COMPANY").
                                       
                                   RECITALS

     WHEREAS, the Purchaser is participating in a private placement by the 
Company pursuant to the Stock Purchase Agreement dated January 12, 1998 (the 
"Purchase Agreement").

     WHEREAS, Chiron owns 280,701 shares of the Common Stock (the "Shares") 
of the Company and;

     WHEREAS, the Purchaser desires to purchase the Shares from Chiron and 
Chiron desires to sell the Shares to the Purchaser, on the terms set forth 
herein.

                                   AGREEMENT

     The Purchaser, the Company (with regard to Section 3 only) and Chiron, 
intending to be legally bound, agree as follows:

     SECTION 1.     SALE AND PURCHASE OF SHARES

     1.1  SALE AND PURCHASE OF THE SHARES.  At the Closing (as defined 
below), Chiron shall sell, assign, transfer and deliver to Purchaser and 
Purchaser agrees to purchase from Chiron the Shares at a purchase price of 
$7.125 per share, on the terms and subject to the conditions set forth in 
this Agreement.

     1.2  PURCHASE PRICE.  The aggregate purchase price payable by the 
Purchaser for the Shares (the "Purchase Price") shall be $1,999,994.63 
delivered to Chiron upon the Closing Date by wire transfer of immediately 
available funds.

     1.3  CLOSING.

          (a)  The closing of the sale of the Shares to the Purchaser (the
"Closing") shall take place at the offices of Cooley Godward LLP, Five Palo
Alto Square, 3000 El Camino Real, Palo Alto, California 94306 on January 12,
1998 (the "Closing Date").

<PAGE>

          (b)  At the Closing:

                   (i)  the Purchaser shall pay to Purchase Price as 
     contemplated by Section 1.2;

                   (ii) Chiron shall deliver to the Company's transfer agent 
     prior to Closing the stock certificates representing the Shares and 
     executed stock powers assigning the Shares to the Purchaser and promptly 
     following the Closing, but in no event later than three days following 
     the Closing, Chiron shall deliver to Purchaser stock certificates 
     representing the Shares registered in the name of Purchaser, or in such 
     nominee name(s) as designated by such Purchaser.

     1.4  ASSIGNMENT OF REGISTRATION RIGHTS.  Chiron hereby assigns its 
registration rights under Sections 6, 7, 8 and 9 of that certain Amended and 
Restated Information and Registration Rights Agreement, as amended (the 
"Registration Agreement") to the Purchaser pursuant to Section 19 of the 
Registration Agreement, but only with respect to the Shares.  Chiron shall 
retain all registration rights under the Registration Agreement with respect 
to the remaining shares of Common Stock of the Company owned by Chiron.

     SECTION 2.     REPRESENTATIONS AND WARRANTIES OF CHIRON

     Chiron represents and warrants to Purchaser as follows:

     2.1  ORGANIZATION. The Company is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware and has
all requisite corporate power and authority and all licenses, permits and
authorizations to conduct its business as it is currently being conducted and
as it is presently proposed to be conducted.

     2.2  AUTHORIZATION; DUE EXECUTION; BINDING OBLIGATIONS.

          (a)  Chiron has full power and authority to execute, deliver and 
perform its obligations under this Agreement and all agreements, instruments 
and documents contemplated hereby, and all action of Chiron necessary for 
such execution, delivery and performance has been duly taken.

          (b)  Chiron's execution, delivery and performance of this Agreement 
have been duly authorized by all requisite corporate and stockholder action 
by Chiron and its stockholders, respectively.  Upon the execution and 
delivery by Chiron, and assuming the valid execution and delivery of this 
Agreement by each of the Purchaser and the Company, this Agreement will 
constitute a valid and binding obligation of Chiron, enforceable in 
accordance with its terms, except as enforceability may be limited by 
applicable bankruptcy, insolvency, reorganization, moratorium or similar laws 
affecting creditors' and contracting parties' rights generally and except as 
enforceability may be subject to general principles of equity (regardless of 
whether such enforceability is considered in a proceeding in equity or at 
law), including specific performance.

     2.3  TITLE TO THE SHARES.  Chiron is the owner, beneficially and of 
record, of the Shares, free and clear of any liens, encumbrances, security 
agreements, equities, options, claims, 

                                       2
<PAGE>

charges or restrictions, and effective with the Closing, Chiron's entire 
right, title and interest in and to the Shares shall have been conveyed to 
the Purchaser.

     2.4  NO CONSENT REQUIRED.  No consent, authorization, approval, order, 
license, certificate or permit or act of or from, or declaration or filing 
with, any foreign, federal, state, local or other governmental authority or 
regulatory body or any court or other tribunal or any party to any contract, 
agreement, instrument, lease or license to which Chiron is a party or to 
which Chiron is subject that is required to be obtained by Chiron for the 
execution, delivery or performance by Chiron of this Agreement or any of the 
other agreements, instruments and documents being or to be executed and 
delivered hereunder or in connection herewith or for the consummation of the 
transactions contemplated hereby, assuming the accuracy of Purchaser's 
representations and warranties in Section 4.3.

     2.5  NO CONFLICTS.  Chiron's execution, delivery and performance of this 
Agreement will not violate, conflict with, result in a breach of or 
constitute (upon notice or lapse of time or both) a default under, or result 
in the creation or imposition of any lien, security interest, mortgage, 
pledge, charge or other encumbrance, of any material nature, upon any 
properties or assets of Chiron under any (a) law, regulation, rule, 
injunction, judgment, order, decree, ruling, charge or other restriction of 
any government, governmental agency, court or arbitrator to which Chiron is 
subject, (b) Chiron's Amended and Restated Certificate of Incorporation or 
Bylaws of Chiron or (c) any provision of any material indenture, mortgage, 
agreement, contract or other material instrument to which Chiron is a party 
or by which Chiron or any of its properties or assets is bound as of the date 
hereof.

     SECTION 3.     REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

     Subject to and except as set forth on the Schedule of Exceptions which 
is arranged in Sections corresponding to the sub-section numbered provisions 
contained below in this Section and except as described in the SEC Reports, 
the Company hereby represents and warrants to, and covenants with, the 
Purchaser as follows:

     3.1  ORGANIZATION AND QUALIFICATION. The Company is a corporation duly 
organized, validly existing and in good standing under the laws of the State 
of Delaware and has all requisite corporate power and authority and all 
licenses, permits and authorizations to conduct its business as it is 
currently being conducted and as it is presently proposed to be conducted.  
The Company is duly qualified and is authorized to transact business and is 
in good standing as a foreign corporation in each jurisdiction in which the 
failure so to qualify would have a material adverse effect on its business, 
assets, liabilities, operations, financial condition or prospects.

     3.2  SEC REPORTS.

          (a)  Since January 1, 1997, the Company has filed with the 
Securities and Exchange Commission (the "SEC") all reports ("SEC Reports") 
required to be filed by it under the Securities Exchange Act of 1934, as 
amended (the "Exchange Act").  All of the SEC Reports filed by the Company 
comply in all material respects with the requirements of the Exchange Act.  
None of the SEC Reports contains, as of the respective dates thereof, any 
untrue statement of a material fact or omits to state any material fact 
required to be stated therein or necessary to make 

                                       3
<PAGE>

the statements therein not misleading in light of the circumstances under 
which they were made.  All financial statements contained in the SEC Reports 
have been prepared in accordance with generally accepted accounting 
principles consistently applied throughout the period indicated ("GAAP").  
Each balance sheet presents fairly in accordance with GAAP the financial 
position of the Company as of the date of such balance sheet, and each 
statement of operations, of stockholders' equity and of cash flows presents 
fairly in accordance with GAAP the results of operations, the stockholders' 
equity and the cash flows of the Company for the periods then ended.

          (b)  The Company has delivered to the Purchaser the following SEC 
Reports:

                   (i)    the Company's Annual Report on Form 10-K for the 
fiscal year ended December 31, 1996 (without exhibits);

                    (ii)  the Company's Quarterly Reports on Form 10-Q as 
filed with the SEC for the quarters ended March 31, 1997, June 30, 1997 and 
September 30, 1997 (without exhibits);

                    (iii) the Company's Proxy Statement for the 1997 Annual 
Meeting of Stockholders.

          (c)  No event has occurred since January 1, 1997, requiring the 
filing of an SEC Report that has not heretofore been filed and furnished to 
the Purchaser (including, without limitation, any amendment to any such SEC 
Report).

     3.3  NO MATERIAL CHANGE.  As of the date hereof, there has been no 
material adverse change in the business, assets, liabilities, financial 
condition, operations or prospects of the Company since September 30, 1997, 
except that the Company continues to incur losses as described in the SEC 
Reports.

     3.4  CAPITALIZATION.  The authorized capital stock of the Company 
consists of (i) 25,000,000 shares of Common Stock, $.001 par value, of which 
9,854,018 such shares were issued and outstanding as of January 9, 1998 and 
(ii) 5,000,000 shares of preferred stock, $.001 par value, of which no shares 
are issued and outstanding on the date hereof.  As of the date hereof, the 
Company has no intention to issue any shares of such Preferred Stock.  Except 
as contemplated by this Agreement, there are no existing options, warrants, 
calls, preemptive (or similar) rights, subscriptions or other rights, 
agreements, arrangements or commitments of any character obligating the 
Company to issue, transfer or sell, or cause to be issued, transferred or 
sold, any shares of capital stock of the Company or other equity interests in 
the Company or any securities convertible into or exchangeable for such 
shares of capital stock or other equity interests, and there are no 
outstanding contractual obligations of the Company to repurchase, redeem or 
otherwise acquire, or prepare and file with the SEC any registration 
statement to register under the Securities Act of 1933, as amended (the 
"Securities Act") with respect to, any such shares of capital stock or other 
equity interests.

     3.5  NASDAQ NATIONAL MARKET.  The Company's Common Stock is listed on 
the Nasdaq National Market, and there are no proceedings to revoke or suspend 
such listing.

                                       4
<PAGE>

     3.6  ABSENCE OF LITIGATION.  There is no action, suit, proceeding or 
investigation pending or, to the Company's best knowledge, that has been 
filed, commenced or threatened, by or before any governmental agency, court 
or arbitrator against the Company which might result either individually or 
in the aggregate, in any material adverse change in the business, assets, 
liabilities, financial condition, operations or prospects of the Company 
(including, without limitation, any such action, suit, proceeding or 
investigation that questions the validity of this Agreement or the issuance 
of the Shares thereunder).

     3.7  INTANGIBLE RIGHTS.  To the Company's best knowledge, the Company 
owns or has the right to use pursuant to valid and enforceable licenses, 
sublicenses, agreements or permissions, all Intangible Rights (as defined 
below) that are necessary or desirable for the conduct of the business of the 
Company as it is currently being conducted and as it is presently proposed to 
be conducted, and no claims adverse to the interests of the Company are 
pending or, to the best knowledge of the Company, have been threatened or 
otherwise asserted with respect to the Company's ownership or use of any such 
Intangible Rights.  To the Company's best knowledge, the Company is not 
infringing any Intangible Right owned or used by any third party nor, to the 
Company's best knowledge, is any third party infringing any Intangible Right 
owned or used by the Company.  For purposes of this Agreement, the term 
"Intangible Rights" means (i) all inventions (whether patentable or 
unpatentable, and whether or not reduced to practice), all improvements 
thereto, and all patents, patent applications, and patent disclosures, 
together with all reissuances, continuations, continuations-in-part, 
revisions, extensions, and reexaminations thereof, (ii) all trademarks, 
service marks, trade dress, logos, trade names and corporate names, together 
with all translations, adaptations, derivations and combinations thereof and 
including all goodwill associated therewith, and all applications, 
registrations and renewals in connection therewith, (c) all copyrightable 
works, all copyrights, all applications, registrations and renewals in 
connection therewith, (iii) all trade secrets and confidential business 
information (including, without limitation, ideas, research and development, 
know-how, formulas, compositions, manufacturing and production processes and 
techniques, technical data, designs, drawings, specifications, supplier 
lists, and business and marketing plans and proposals), (iv) all computer 
software (including, data and related documentation), (v) all other 
proprietary rights and (vi) all copies and tangible embodiments of any of the 
foregoing (in whatever form or medium).

     3.8  LEGAL COMPLIANCE.  The Company has not violated any applicable laws 
(including, without limitation, all rules, regulations, codes, plans, 
injunctions, judgments, orders, decrees, rulings and charges thereunder) of 
federal, state, local and foreign governments (and all agencies thereof) in 
respect of the conduct of its business or the ownership of its properties 
which violation would (either individually or in the aggregate) materially 
and adversely affect the business, assets, liabilities, financial condition, 
operations or prospects of the Company.

     3.9  CERTAIN AGREEMENTS.  All of the collaborative agreements, research
and development agreements, licensing agreements and other agreements with
corporate partners and governmental or educational entities that have been
previously disclosed by the Company in the SEC Reports referred to in paragraph
(b) of Section 4.5 hereof are valid and enforceable obligations of the Company
and, to the Company's best knowledge, the other parties thereto.  Except for
breaches and defaults that would not, singly or in the aggregate, have a
material adverse effect on the Company or its assets, liabilities, operations,
financial condition, business or prospects, the Company is not in breach or
default under any such contracts or agreements nor 

                                       5
<PAGE>

has any event occurred which, with the giving of notice or the passage of 
time or both, would constitute a breach or default on the Company's part 
thereunder.  To the Company's best knowledge, none of the other parties to 
such contracts or agreements is in breach or default thereunder nor has any 
event occurred which, with the giving of notice or the passage of time or 
both, would constitute a breach or default on such other parties' part.

     3.10 REGISTRATION.  The Company acknowledges and agrees that the 
execution and delivery of this  Agreement by the Purchaser constitutes the 
Purchaser's notice pursuant to its rights under the Registration Agreement to 
have the Shares registered under the Registration Statement (as defined in 
the Purchase Agreement).

    SECTION 4.      REPRESENTATIONS AND WARRANTIES OF THE PURCHASER

     The Purchaser represents and warrants, to and for the benefit of Chiron, 
as follows:

     4.1  AUTHORITY, APPROVAL AND ENFORCEABILITY.

          (a)  Purchaser has full power and authority to execute, deliver and 
perform its obligations under this Agreement and all agreements, instruments 
and documents contemplated hereby, and all action of Purchaser necessary for 
such execution, delivery and performance has been duly taken.

          (b)  Purchaser's execution, delivery and performance of this 
Agreement have been duly authorized by all requisite action by Purchaser, 
respectively.  Upon the execution and delivery by Purchaser, and assuming the 
valid execution and delivery of this Agreement by each of the Purchaser and 
the Company, this Agreement will constitute a valid and binding obligation of 
Purchaser, enforceable in accordance with its terms, except as enforceability 
may be limited by applicable bankruptcy, insolvency, reorganization, 
moratorium or similar laws affecting creditors' and contracting parties' 
rights generally and except as enforceability may be subject to general 
principles of equity (regardless of whether such enforceability is considered 
in a proceeding in equity or at law), including specific performance.

     4.2  NO CONSENT REQUIRED.  No consent, authorization, approval, order, 
license, certificate or permit or act of or from, or declaration or filing 
with, any foreign, federal, state, local or other governmental authority or 
regulatory body or any court or other tribunal or any party to any contract, 
agreement, instrument, lease or license to which Purchaser is a party or to 
which Purchaser is subject that is required for the execution, delivery or 
performance by Purchaser of this Agreement or any of the other agreements, 
instruments and documents being or to be executed and delivered hereunder or 
in connection herewith or for the consummation of the transactions 
contemplated hereby.

     4.3  INVESTMENT REPRESENTATIONS.  Purchaser understands that the Shares 
have not been registered under the Securities Act of 1933, as amended (the 
"Securities Act") and shall continue to bear the Securities Act legend. 
Purchaser also understands that the Shares are being offered and sold 
pursuant to an exemption from registration contained in the Securities Act 
based in part upon Purchaser's representations contained in the Agreement.  
Purchaser hereby represents and warrants as follows:

                                       6
<PAGE>

          (a)  PURCHASER BEARS ECONOMIC RISK.  Purchaser has substantial 
experience in evaluating and investing in private placement transactions of 
securities in companies similar to the Company so that it is capable of 
evaluating the merits and risks of its investment in the Company and has the 
capacity to protect its own interests.  Purchaser must bear the economic risk 
of this investment indefinitely unless the Shares are registered pursuant to 
the Securities Act, or an exemption from registration is available.  
Purchaser understands that the Company has no present intention of 
registering the Shares.  Purchaser also understands that there is no 
assurance that any exemption from registration under the Securities Act will 
be available and that, even if available, such exemption may not allow the 
Company to transfer all or any portion of the Shares under the circumstances, 
in the amounts or at the times Purchaser might propose.

          (b)  ACCREDITED INVESTOR.  Purchaser represents that it is an 
accredited investor within the meaning of Regulation D under the Securities 
Act.

          (c)  COMPANY INFORMATION.  Purchaser is familiar with the Company's 
business, management, financial affairs, operations and facilities.

          (d)  RULE 144.  Purchaser acknowledges and agrees that the Shares 
must be held indefinitely unless they are subsequently registered under the 
Securities Act or an exemption from such registration is available.  
Purchaser has been advised or is aware of the provisions of Rule 144 
promulgated under the Securities Act, which permits limited resale of shares 
purchased in a private placement subject to the satisfaction of certain 
conditions, including, among other things:  the availability of certain 
current public information about the Company, the resale occurring not less 
than one year after a party has purchased and paid for the security to be 
sold, the sale being through an unsolicited "broker's transaction" or in 
transactions directly with a market maker (as said term is defined under the 
Securities Exchange Act of 1934, as amended) and the number of shares being 
sold during any three-month period not exceeding specified limitations.

     SECTION 5.     SURVIVAL OF REPRESENTATIONS, WARRANTIES AND AGREEMENTS. 
Notwithstanding any investigation made by any party to this Agreement, all 
covenants, agreements, representations and warranties made by the Company, 
Chiron, and Purchaser herein shall survive the execution of this Agreement 
and the sale to the Purchaser of the Shares and shall terminate upon the 
subsequent transfer of the Shares.

     SECTION 6.     CONDITIONS TO CHIRON'S OBLIGATIONS AT THE CLOSING. 
Chiron's obligation to complete the sale and issuance of the Shares at 
Closing shall be subject to the following conditions to the extent not waived 
by Chiron:

     6.1  REPRESENTATIONS AND WARRANTIES CORRECT.  The representations and 
warranties made by Purchaser in Section 4 hereof shall be true and correct 
when made, and shall be true and correct on the Closing Date.

     6.2  COVENANTS PERFORMED.  All covenants, agreements and conditions 
contained herein to be performed by the Purchaser on or prior to the Closing 
Date shall have been performed or complied with in all material respects.

                                       7
<PAGE>

     6.3  QUALIFICATIONS, LEGAL INVESTMENT.  All authorizations, approvals, 
or permits, if any, of any governmental authority or regulatory body of the 
United States or of any state that are binding upon the Purchaser and that 
are required in connection with the lawful sale of the Shares at such Closing 
pursuant to this Agreement shall have been duly obtained and shall be 
effective on and as of the date of such Closing.  No stop order or other 
order enjoining the sale of the Shares shall have been issued and no 
proceedings for such purpose shall be pending or, to the knowledge of Chiron, 
threatened by the SEC or any commissioner of corporations or similar officer 
of any state having jurisdiction over this transaction.  At the time of such 
Closing, the sale of the Shares to be purchased and sold at such Closing 
shall be legally permitted by all laws and regulations to which the Purchaser 
and Chiron are subject.

     SECTION 7.     CONDITIONS TO PURCHASER'S OBLIGATIONS AT THE CLOSING. 
Purchaser's obligation to purchase the Shares at the Closing thereby shall be 
subject to the following conditions to the extent not waived by the Purchaser:

     7.1  REPRESENTATIONS AND WARRANTIES CORRECT.  The representations and 
warranties made by the Company in Section 3 hereof and by Chiron in Section 2 
hereof shall be true and correct when made, and shall be true and correct as 
of the Closing Date.

     7.2  COVENANTS PERFORMED.  All covenants, agreements and conditions 
contained herein to be performed by the Company and Chiron shall have been 
performed or complied with in all material respects.

     7.3  QUALIFICATIONS, LEGAL INVESTMENT.  All authorizations, approvals, 
or permits, if any, of any governmental authority or regulatory body of the 
United States or of any state that are binding upon Chiron and that are 
required in connection with the lawful sale of the Shares at such Closing 
pursuant to this Agreement shall have been duly obtained and shall be 
effective on and as of the Closing Date.  No stop order or other order 
enjoining the sale of the Shares shall have been issued and no proceedings 
for such purpose shall be pending or, to the knowledge of Chiron, threatened 
by the SEC, or any commissioner of corporations or similar officer of any 
state having jurisdiction over this transaction.  At the time of the Closing, 
the sale of the Shares shall be legally permitted by all laws and regulations 
to which the Purchaser and Chiron are subject.

     7.4  CLOSING OF PRIVATE PLACEMENT.  The private placement by the Company 
of 1,403,508 shares of its Common Stock pursuant to the Purchase Agreement 
shall have closed.

     7.5  NO MATERIAL ADVERSE CHANGE.  There shall have been no material 
adverse change in the business, assets, liabilities, operations or financial 
condition of the Company since the date of this Agreement.

     7.6  NO LITIGATION.  Since the date of this Agreement, no proceeding 
challenging this Agreement or the transactions contemplated hereby, or 
seeking to prohibit, alter, prevent or materially delay the Closing or the 
performance by the Company of any of its obligations hereunder, shall have 
been instituted before any governmental agency, court or arbitrator and shall 
be pending.

                                       8
<PAGE>

     SECTION 8.     MISCELLANEOUS PROVISIONS

     8.1  GOVERNING LAW.  This Agreement shall be governed in all respects by 
the laws of the State of California as such laws are applied to agreements 
between California residents entered into and performed entirely in 
California.

     8.2  ENTIRE AGREEMENT.  This Agreement and the Exhibits hereto and the 
other documents delivered pursuant hereto constitute the full and entire 
understanding and agreement between the parties with regard to the subjects 
hereof and no party shall be liable or bound to any other in any manner by 
any representations, warranties, covenants and agreements except as 
specifically set forth herein and therein.

     8.3  DELAYS OR OMISSIONS.  It is agreed that no delay or omission to 
exercise any right, power or remedy accruing to any party, upon any breach, 
default or noncompliance  by another party under this Agreement, shall impair 
any such right, power or remedy, nor shall it be construed to be a waiver of 
any such breach, default or noncompliance, or any acquiescence therein, or of 
or in any similar breach, default or noncompliance thereafter occurring. It 
is further agreed that any waiver, permit, consent or approval of any kind or 
character of any breach, default or noncompliance under this Agreement or any 
waiver of any provisions or conditions of the Agreement must be in writing 
and shall be effective only to the extent specifically set forth in such 
writing. All remedies, either under this Agreement or otherwise afforded to 
any party, shall be cumulative and not alternative.

     8.4  NOTICES.  All notices, requests, demands and other communications 
required or permitted under this Agreement and the transactions contemplated 
herein shall be in writing and shall be deemed to have been duly given, made 
and received on the date when delivered by hand delivery with receipt 
acknowledged, or upon the next business day following receipt of telex or 
telecopy transmission, or upon the third day after deposit in the United 
States mail, registered or certified with postage prepaid, return receipt 
requested, addressed as set forth on the signature page.

Any party may alter the addresses to which communications or copies are to be 
sent by giving notice of such change of address in conformity with the 
provisions of this Section 8.4 for the giving of notice.

     8.5  ASSIGNMENT:  BINDING UPON SUCCESSORS AND ASSIGNS.  None of the 
parties hereto may assign any of its rights or obligations hereunder without 
the prior written consent of the other party hereto.  This Agreement will be 
binding upon and inure to the benefit of the parties hereto and their 
respective successors and permitted assigns.

     8.6  AMENDMENT AND WAIVERS.  Any term or provision of this Agreement may 
be amended, and the observance of any term of this Agreement may be waived 
(either generally or in a particular instance and either retroactively or 
prospectively) only by a writing signed by the party to be bound thereby.  
The waiver by a party of any breach hereof or default in the performance 
hereof will not be deemed to constitute a waiver of any other default or any 
succeeding breach or default.

                                       9
<PAGE>

     8.7  EXPENSES.  Each party will bear its respective expenses and legal 
fees incurred with respect to this Agreement, and the transactions 
contemplated hereby including any broker's fees for which they are 
responsible.

     8.8  ENTIRE AGREEMENT.  This Agreement and the exhibits hereto 
constitute the entire understanding and agreement of the parties hereto with 
respect to the subject matter hereof and supersede all prior and 
contemporaneous agreements or understandings, inducements or conditions, 
express or implied, written or oral, between the parties with respect hereto, 
which shall remain in full force and effect.  The express terms hereof 
control and supersede any course of performance or usage of the trade 
inconsistent with any of the terms hereof.

     8.9  TITLES AND SUBTITLES.  The titles of the sections and subsections 
of the Agreement are for convenience of reference only and are not to be 
considered in construing this Agreement.

     8.10 SEVERABILITY.  If any provision of this Agreement, or the 
application thereof, will for any reason and to any extent be invalid or 
unenforceable, the remainder of this Agreement and application of such 
provision to other persons or circumstances will be interpreted so as 
reasonably to effect the intent of the parties hereto.  The parties further 
agree to replace such void or unenforceable provision of this Agreement with 
a valid and enforceable provision that will achieve, to the greatest extent 
possible, the economic, business and other purposes of the void or 
unenforceable provision.

     8.11 COUNTERPARTS.  This Agreement may be executed in any number of 
counterparts, each of which shall be an original, but all of which together 
shall constitute one instrument.

                                       10
<PAGE>

     THE PARTIES HERETO HAVE CAUSED THIS AGREEMENT TO BE EXECUTED AND 
DELIVERED AS OF JANUARY 12, 1998.

<TABLE>
<CAPTION>
"CHIRON":                         CHIRON CORPORATION
<S>                              <C>

                                  BY: /s/ James Kent
                                     -------------------------------------
                                  TITLE:  Vice President and Treasurer
                                        ----------------------------------

"PURCHASER":                      LOMBARD ODIER & CIE


                                  BY: /s/ Daniel Malfani
                                     -------------------------------------
                                  TITLE:  Assistant Vice President
                                        ----------------------------------

                                  BY: /s/ Rene-Alain Walthert
                                     -------------------------------------
                                  TITLE:  Assistant Manager
                                        ----------------------------------

"COMPANY"                         ONYX PHARMACEUTICALS, INC.


                                  BY: /s/ Hollings C. Renton
                                       -------------------------------------
                                  TITLE:   President and Chief Executive Officer
                                        ----------------------------------
</TABLE>
                                       11

<PAGE>

                                                                  Exhibit 5.1


[COOLEY GODWARD LLP LETTERHEAD]

April 2, 1998



ONYX Pharmaceuticals, Inc.
3031 Research Drive
Richmond, CA  94806



Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection 
with the filing by ONYX Pharmaceuticals, Inc., a Delaware corporation (the 
"Company"), of a Resale Registration Statement on Form S-3 (the "Registration 
Statement") with the Securities and Exchange Commission (the "Commission") on 
April 2, 1998 covering the offering of up to 1,684,209 shares of the 
Company's common stock, par value of $.001 per share (the "Shares").  All of 
the Shares are to be sold by certain stockholders as described in the 
Registration Statement.

In connection with this opinion, we have examined and relied upon the 
Registration Statement and related Prospectus included therein, the Company's 
Restated Certificate of Incorporation and Bylaws, and the originals or copies 
certified to our satisfaction of such records, documents, certificates, 
memoranda and other instruments as in our judgment are necessary or 
appropriate to enable us to render the opinion expressed below.  We have 
assumed the genuineness and authenticity of all documents submitted to us as 
originals, and the conformity to originals of all documents where due 
execution and delivery are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion 
that the Shares are validly issued, fully paid and nonassessable.

We consent to the reference to our firm under the caption "Legal Matters" in 
the Prospectus included in the Registration Statement and to the filing of 
this opinion as an exhibit to the Registration Statement.

Sincerely,

Cooley Godward LLP


By: /s/ Deborah A. Marshall
    ------------------------
    Deborah A. Marshall


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