Document:

<PAGE>

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED (THE "1933 ACT"), OR ANY APPLICABLE STATE SECURITIES LAWS, AND MAY
NOT BE SOLD OR TRANSFERRED UNLESS SUCH SALE OR TRANSFER IS IN ACCORDANCE WITH
THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS OR SOME OTHER
EXEMPTION FROM THE REGISTRATION REQUIREMENTS OF SUCH ACT AND APPLICABLE LAWS
IS AVAILABLE WITH RESPECT THERETO.

                          PREFERRED STOCK PURCHASE WARRANT

Warrant No. _________                                  Number of Shares: 131,578
                                                       Series C Preferred Stock

                           RIGEL PHARMACEUTICALS, INC.

                             Void after June 30, 2005

     1.   ISSUANCE. This Warrant is issued to LIGHTHOUSE CAPITAL PARTNERS II,
L.P. by RIGEL PHARMACEUTICALS, INC., a Delaware corporation (hereinafter with
its successors called the "COMPANY").

     2.   PURCHASE PRICE; NUMBER OF SHARES. The registered holder of this
Warrant (the "HOLDER"), commencing on the date hereof, is entitled upon
surrender of this Warrant with the subscription form annexed hereto duly
executed, at the principal office of the Company, to purchase from the
Company the following securities (collectively, the "SHARES") at a price per
share of $1.14 (the "PURCHASE PRICE"), 131,578 fully paid and nonassessable
shares of Series C Preferred Stock, $.001 par value, of the Company (the
"PREFERRED STOCK"). Until such time as this Warrant is exercised in full or
expires, the Purchase Price and the securities issuable upon exercise of this
Warrant are subject to adjustment as hereinafter provided. The person or
persons on whose name or names any certificate representing shares of
Preferred Stock is issued hereunder shall be deemed to have become the holder
of record of the shares represented thereby as at the close of business on
the date this Warrant is exercised with respect to such shares, whether or
not the transfer books of the Company shall be closed.

     3.   PAYMENT OF THE PURCHASE PRICE. The Purchase Price may be paid (i)
in cash or by check, (ii) by the surrender by the Holder to the Company of
any promissory notes or other obligations issued by the Company, with all
such notes and obligations so surrendered being credited against the Purchase
Price in an amount equal to the principal amount thereof plus accrued
interest to the date of surrender, or (iii) by any combination of the
foregoing.

     4.   NET ISSUE ELECTION. The Holder may elect to receive, without the
payment by the Holder of any additional consideration, shares of Preferred
Stock equal to the value of this Warrant or any portion hereof by the
surrender of this Warrant or such portion to the Company, with the net issue
election notice annexed hereto duly executed, at the principal office of the
Company. Thereupon, the Company shall issue to the Holder such number of
fully paid and nonassessable shares of Preferred Stock as is computer using
the following formula:
                                   Y (A - B)
                               X = ---------
                                       A

                                       1.
<PAGE>

where:    X=   the number of shares of Preferred Stock to be issued to the
               Holder pursuant to this SECTION 4.

          Y=   the number of shares of Preferred Stock covered by this Warrant
               in respect of which the net issue election is made pursuant to
               this SECTION 4.

          A=   the Fair Market Value (defined below) of one share of Preferred
               Stock, as determined at the time the net issue election is made
               pursuant to this SECTION 4.

          B=   the Purchase Price in effect under this Warrant at the time the
               net issue election is made pursuant to this SECTION 4.

"Fair Market Value" of a share of Preferred Stock (or Common Stock if the
Preferred Stock has been automatically converted into Common Stock) as a
particular date (the "Determination Date") shall mean:

          (i)  If the net issue election is made in connection with and
     contingent upon the closing of the sale of the Company's Common Stock to
     the public in a public offering pursuant to a Registration Statement under
     the Act (a "Public Offering"), and if the Company's Registration Statement
     relating to such Public Offering ("Registration Statement") has been
     declared effective by the SEC, the initial "Price to Public" specified in
     the final prospectus with respect to such offering multiplied by the number
     of shares of Common Stock into which each share of Preferred Stock is then
     convertible.

          (ii) If the net issue election is not made in connection with and
     contingent upon a Public Offering, then as follows:

               (A)  If traded on a securities exchange or the Nasdaq National
          Market, the fair market value of the Common Stock shall be deemed to
          be the average of the closing or last reported sale prices of the
          Common Stock on such exchange or market over the 30-day period ending
          five business days prior to the Determination Date, and the fair
          market value of the Preferred Stock shall be deemed to be such fair
          market value of the Common Stock multiplied by the number of shares of
          Common Stock into which each share of Preferred Stock is then
          convertible;

               (B)  If otherwise traded in an over-the-counter market, the fair
          market value of the Common Stock shall be deemed to be the average of
          the closing ask prices of the Common Stock over the 30-day period
          ending five business days prior to the Determination Date, and the
          fair market value of the Preferred Stock shall be deemed to be such
          fair market value of the Common Stock multiplied by the number of
          shares of Common Stock into which each share of Preferred Stock is
          then convertible; and

               (C)  If there is no public market for the Common Stock, then fair
          market value shall be determined in good faith by the Company's Board
          of Directors.

     5.   PARTIAL EXERCISE. This Warrant may be exercised in part, and the
Holder shall be entitled to receive a new warrant, which shall be dated as of
the date of this Warrant, covering the number of shares in respect of which
this Warrant shall not have been exercised.

     6.   FRACTIONAL SHARES. In no event shall any fractional share of
Preferred Stock be issued upon any exercise of this Warrant. If, upon
exercise of this Warrant as an entirety, the Holder would, except as provided
in this Section 6, be entitled to receive a fractional share of Preferred
Stock, then the Company shall pay in lieu thereof, the Fair Market Value of
such fractional share in cash.

     7.   EXPIRATION DATE; AUTOMATIC EXERCISE. Except as otherwise set forth
in SECTION 11, this Warrant shall expire at the close of business on June 30,
2005 and shall be void thereafter. Notwithstanding the foregoing, this
Warrant shall automatically be deemed to be exercised in full pursuant to the
provisions of SECTION 4 hereof, without any

                                       2.
<PAGE>

further action on behalf of the Holder, immediately prior to the time this
Warrant would otherwise expire pursuant to the preceding sentence or pursuant
to SECTION 11.

     8.   RESERVED SHARES; VALID ISSUANCE. The Company covenants that it will
at all times from and after the date hereof reserve and keep available such
number of its authorized shares of Preferred Stock and Common Stock, $.001
par value, of the Company (the "COMMON STOCK"), free from all preemptive or
similar rights therein, as will be sufficient to permit, respectively, the
exercise of this Warrant in full and the conversion into shares of Common
Stock of all shares of Preferred Stock receivable upon such exercise. The
Company further covenants that such shares as may be issued pursuant to such
exercise and/or conversion will, upon issuance, be duly and validly issued,
fully paid and nonassessable and free from all takes, liens and charges with
respect to the issuance thereof.

     9.   STOCK SPLITS AND DIVIDENDS. If after the date hereof the Company
shall subdivide the Preferred Stock, by split-up or otherwise, or combine the
Preferred Stock, or issue additional shares of Preferred Stock in payment of
a stock dividend on the Preferred Stock, the number of shares of Preferred
Stock issuable in the exercise of this Warrant shall forthwith be
proportionately increased in the case of a subdivision or stock dividend, or
proportionately increased in the case of a combination, and the Purchase
Price shall forthwith be proportionately decreased in the case of a
subdivision or stock dividend, or proportionately increased in the case of a
combination.

     10.  ADJUSTMENTS FOR DILUTING ISSUANCES. The other antidilution rights
applicable to the Preferred Stock and the Common Stock of the Company are set
forth in the Amended and Restated Certificate of Incorporation, as amended
from time to time (the "Articles"), a true and complete copy in its current
form which is attached hereto as EXHIBIT A. Such rights shall not be
restated, amended or modified in any manner which effects the Holder
differently than the holders of Series C Preferred without such Holder's
prior written consent. The Company shall promptly provide the Holder hereof
with any restatement, amendment or modification to the Articles promptly
after the same has been made.

     11.  MERGERS AND RECLASSIFICATION. If after the date hereof the Company
shall enter into any Reorganization (as hereinafter defined), then, as a
condition of such Reorganization, lawful provisions shall be made, and duly
executed documents evidencing the same from the Company or its successor
shall be delivered to the Holder, so that the Holder shall thereafter have
the right to purchase, at a total price not to exceed that payable upon the
exercise of this Warrant in full, the kind and amount of shares of stock and
other securities and property receivable upon such Reorganization by a holder
of the number of shares of Preferred Stock which might have been purchased by
the Holder immediately prior to such Reorganization, and in any such case
appropriate provisions shall be made with respect to the rights and interest
of the Holder to the end that the provisions hereof (including without
limitation, provisions for the adjustment of the Purchase Price and the
number of shares issuable hereunder and the provisions relating to the net
issue election) shall thereafter be applicable in relation to any shares of
stock or other securities and property thereafter deliverable upon exercise
hereof. For the purposes of this SECTION 11, the term "REORGANIZATION" shall
include without limitation any reclassification, capital reorganization or
change of the Preferred Stock (other than as a result of a subdivision,
combination or stock dividend provided for in SECTION 9 hereof), or any
consolidation of the Company with, or merger of the Company into, another
corporation or other business organization (other than a merger in which the
Company is the surviving corporation and which does not result in any
reclassification or change of the outstanding Preferred Stock), or any sale
or conveyance to another corporation or other business organization of all or
substantially all of the assets of the Company.

     Notwithstanding the term of this Warrant fixed pursuant to SECTION 7
above and the provisions of this SECTION 11, the right to purchase Preferred
Stock as granted herein shall expire, to the extent not previously exercised,
immediately upon the closing of a merger or consolidation of the Company with
or into another corporation when the Company is not the surviving corporation
(other than a merger or consolidation for the principal purpose of changing
the domicile of the Company), or the sale of all or substantially all of the
Company's capital stock, properties and assets to any other person, in each
case where the stockholders of the Company immediately prior to such merger,
consolidation or sale of assets own (directly or indirectly) less than 50% of
the voting securities of the surviving entity or purchaser of assets in such
transaction (collectively, a "Merger"), except to the extent assumed by the
successor corporation (or parent thereof) in connection with such Merger. In
the event that any outstanding warrants to purchase equity securities of the
Company are assumed, this Warrant shall also be similarly assumed.

                                       3.
<PAGE>

     The Company shall notify the Holder within twenty (20) days of any
proposed Merger, and if the Company fails to deliver such notice, then
notwithstanding anything to the contrary in this Warrant, the rights to
purchase the Company's Preferred Stock (or the share of stock and other
securities and property receivable upon such Merger by a holder of the
Preferred Stock (the "OTHER CONSIDERATION")) shall not expire. The Holder may
exercise the Warrant contingent upon the closing of the Merger. If the Merger
does not close within 60 days after notice, any contingent exercise shall be
void.

     12.  CERTIFICATE OF ADJUSTMENT. Whenever the Purchase Price is adjusted,
as herein provided, the Company shall promptly deliver to the Holder a
certificate of the Company's chief financial officer setting forth the
Purchase Price after such adjustment and setting forth a brief statement of
the facts requiring such adjustment.

     13.  NOTICES OF RECORD DATE, ETC. In the event of:

          (a)  any taking by the Company of a record of the holders of any
class of securities for the purpose of determining the holders thereof who
are entitled to receive any dividend or other distribution, or any right to
subscribe for, purchase, sell or otherwise acquire or dispose of any shares
of stock of any class or any other securities or property, or to receive any
other right;

          (b)  any reclassification of the capital stock of the Company,
capital reorganization of the Company, consolidation or merger involving the
Company, or sale or conveyance of all or substantially all of its assets; or

          (c)  any voluntary or involuntary dissolution, liquidation or
winding-up of the Company;

then in such event the Company will provide or cause to be provided to the
Holder a written notice thereof. Such notice shall be provided at least
twenty (20) business days prior to the date specified in such notice on which
any such action is to be taken.

     14.  REPRESENTATIONS, WARRANTIES AND COVENANTS.  This warrant is issued
and delivered by the Company and accepted by each Holder on the basis of the
following representations, warranties and covenants made by the Company:

          A.   The Company has all necessary authority to issue, execute and
deliver this Warrant and to perform its obligations hereunder. This Warrant
has been duly authorized, issued, executed and delivered by the Company and
is the valid and binding obligation of the Company, enforceable in accordance
with its terms, except as enforceability may be limited by bankruptcy,
insolvency, reorganization or other similar laws of general application
affecting the enforcement of Holders rights or by general equity principals
or public policy concerns.

          B.   The shares of Preferred Stock issuable upon the exercise of
this Warrant have been duly authorized and reserved for issuance by the
Company and, when issued in accordance with the terms hereof, will be validly
issued, fully paid and nonassessable.

          C.   The issuance, execution and delivery of this Warrant do not,
and the issuance of the shares of Preferred Stock upon the exercise of this
Warrant in accordance with the terms hereof will not, (i) violate or
contravene the Company's Articles or by-laws, or any law, statute,
regulations, rule, judgment or order applicable to the Company, (ii) violate,
contravene or result in a breach or default under any material contract,
agreement or instrument to which the Company is a party or by which the
Company or any of its assets are bound or (iii) require the consent or
approval of or the filing of any notice or registration with any person or
entity.

          D.   So long as this Warrant has not terminated, Holder shall be
entitled to receive such financial and other information as the Holder would
be entitled to receive under the Series C Preferred Stock Purchase Agreement
if Holder were a holder of that number of shares issuable upon full exercise
of this Warrant.

          E.   As of the date hereof, the authorized capital stock of the
Company consists of (i) 20,000,000 shares of Common Stock, of which 2,510,000
are issued and outstanding shares, 175,000 shares are reserved for

                                       4.
<PAGE>

issuance upon the exercise of that certain Warrant dated May 23, 1997, and
131,578 shares are reserved for issuance upon the exercise of this Warrant
and the conversion of the Preferred Stock, (ii) 665,000 shares of Series A
Preferred Stock, of which 665,000 are issued and outstanding shares, and
(iii) 7,675,000 shares of Series B Preferred Stock, of which 7,500,000 are
issued and outstanding shares, and 175,000 shares are reserved for issuance
upon the exercise of that certain Warrant dated May 23, 1997 and (iv)
8,000,000 shares of Series C Preferred Stock, of which 7,386,843 are issued
and outstanding shares, and 131,578 shares are reserved for issuance upon the
exercise of this Warrant. Attached hereto as EXHIBIT B is a capitalization
table summarizing the capitalization of the Company.

     15.  REGISTRATION RIGHTS.  The Company grants to the Holder registration
rights contained in SECTIONS 2.2, 2.3 and 2.4 of the Company's Amended and
Restated Investor Rights Agreement dated as of November 3, 1997 (the
"INVESTOR RIGHTS AGREEMENT"), so that (i) the shares of Common Stock issuable
upon conversion of the shares of Preferred Stock issuable upon exercise of
this Warrant shall be "Registrable Securities," and (ii) the Holder shall be
a "Holder" and "Investor" for all purposes of such Investor Rights Agreement.

     16.  AMENDMENT. The terms of this Warrant may be amended, modified or
waived only with the written consent of the Holder.

     17.  REPRESENTATIONS AND COVENANTS OF THE HOLDER. The Preferred Stock
Purchase Warrant has been entered into by the Company in reliance upon the
following representations and covenants of the Holder, which by its execution
hereof the Holder hereby confirms:

          A.   INVESTMENT PURPOSE. The right to acquire Preferred Stock or
the Preferred Stock issuable upon exercise of the Holders' rights contained
herein will be acquired for investment and not with a view to the sale or
distribution of any part thereof, and the Holder has not present intention of
selling or engaging in any public distribution of the same except pursuant to
a registration or exemption.

          B.   ACCREDITED INVESTOR. Holder is an "accredited investor" within
the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.

          C.   PRIVATE ISSUE. The Holder understands (i) that the Preferred
Stock issuable upon exercise of the Holder's rights contained herein is not
registered under the 1933 Act or qualified under applicable state securities
laws on the ground that the issuance contemplated by this Warrant will be
exempt from the registration and qualifications requirements thereof, and
(ii) that the Company's reliance on such exemption is predicated on the
representations set forth in this SECTION 17.

          D.   FINANCIAL RISK. The Holder has such knowledge and experience
in financial and business matters as to be capable of evaluating the merits
and risks of its investment and has the ability to bear the economic risks of
its investment.

     18.  NOTICES, TRANSFERS, ETC.

          A.   Any notice or written communication required or permitted to
be given to the Holder may be given by certified mail or delivered to the
Holder at the address most recently provided by the Holder to the Company.

          B.   Subject to compliance with applicable federal and state
securities laws, this Warrant may be transferred by the Holder with respect
to any or all of the shares purchasable hereunder. Upon surrender of this
Warrant to the Company, together with the assignment notice annexed hereto
duly executed, for transfer of this Warrant as an entirety by the Holder, the
Company shall issue a new warrant of the same denomination to the assignee.
Upon surrender of this Warrant to the Company, together with the assignment
hereof properly endorsed by the Holder for transfer with respect to a portion
of the shares of the Preferred Stock purchasable hereunder, the Company shall
issue a new warrant to the assignee, in such denomination as shall be
requested by the Holder hereof, and shall issue to such Holder a new warrant
covering the number of shares in respect of which this Warrant shall not have
been transferred.

          C.   In case this Warrant shall be mutilated, lost, stolen or
destroyed, the Company shall issue a new warrant of like tenor and
denomination and deliver the same (i) in exchange and substitution for and
upon surrender

                                       5.
<PAGE>

and cancellation of any mutilated Warrant, or (ii) in lieu of any Warrant
lost, stolen or destroyed, upon receipt of any affidavit of the Holder or
other evidence reasonably satisfactory to the Company of the loss, theft or
destruction of such Warrant and an indemnification of loss by the Holder in
favor of the Company.

     19.  NO IMPAIRMENT. The Company will not, by amendment of its Articles
or through any reclassification, capital reorganization, consolidation,
merger, sale or conveyance of assets, dissolution, liquidation, issue or sale
of securities or any other voluntary action, avoid or seek to avoid the
observance of performance of any of the terms of this Warrant, but will at
all times in good faith assist in the carrying out of all such terms and in
the taking of all such action as may be necessary or appropriate in order to
protect the rights of the Holder.

     20.  GOVERNING LAW. The provisions and terms of this Warrant shall be
governed by and construed in accordance with the internal laws of the State
of California.

     21.  SUCCESSORS AND ASSIGNS. This Warrant shall be binding upon the
Company's successors and assigns and shall inure to the benefit of the
Holder's successors, legal representatives and permitted assigns.

     22.  BUSINESS DAYS. If the last or appointed day for the taking of any
action required or the expiration of any rights granted herein shall be a
Saturday or Sunday or a legal holiday in California, then such action may be
taken or right may be exercised on the next succeeding day which is not a
Saturday or Sunday or such a legal holiday.

     23.  QUALIFYING PUBLIC OFFERING. If the Company shall effect a firm
commitment underwritten public offering of shares of Common Stock which
results in the conversion of the Preferred Stock into Common Stock pursuant
to the Company's Articles in effect immediately prior to such offering, then,
effective upon such conversion, this Warrant shall change from the right to
Purchase shares of Preferred Stock to the right to purchase shares of Common
Stock, and the Holder shall thereupon have the right to purchase, at a total
price equal to that payable upon the exercise of this Warrant in full, the
number of shares of Common Stock which would have been receivable by the
Holder upon the exercise of this Warrant for shares of Preferred Stock
immediately prior to such conversion of such shares of Preferred Stock into
shares of Common Stock, and in such event appropriate provisions shall be
made with respect to the rights and interest of the Holder to the end that
the provisions hereof (including, without limitation, the provisions for the
adjustment of the Purchase Price and of the number of shares purchasable upon
exercise of this Warrant and the provisions relating to the net issue
election) shall thereafter be applicable to any shares of Common Stock
deliverable upon the exercise hereof.

     24.  VALUE. The Company and the Holder agree that the value of this
Warrant on the date of grant is $100.

Dated: July 16, 1998                   RIGEL PHARMACEUTICALS, INC.

                                       By:  /s/ Nancy Montgomery
                                          ------------------------------------

                                       Name:     Nancy Montgomery
                                            ----------------------------------

                                       Title:    Chief Financial Officer
                                             ---------------------------------
Attest:

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

                                       6.<PAGE>

                                                                  NO. PDW-____

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR INVESTMENT
AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR ANY STATE
SECURITIES LAWS. SUCH SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE
OF SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT AND ANY APPLICABLE
STATE SECURITIES LAWS.

                              WARRANT TO PURCHASE SHARES
                            OF SERIES D PREFERRED STOCK OF
                              RIGEL PHARMACEUTICALS, INC.
                            (VOID AFTER DECEMBER __, 2003)

         This certifies that __________________ or its assigns (the
"Holder"), for value received, is entitled to purchase from RIGEL
PHARMACEUTICALS, INC., a Delaware corporation (the "Company"), up to the
Maximum Purchase Amount (as defined below) of fully paid and nonassessable
shares of the Company's Series D Preferred Stock ("Preferred Stock") for
cash, unless exercised as provided in Section 1.2 of this Warrant, at a price
equal to the price at which the Company first sells shares of it Series D
Preferred Stock after the date of this Warrant, but not greater than Two
Dollars ($2.00) per share prior to any adjustments made pursuant to Section 3
of this Warrant (the "Stock Purchase Price") at any time or from time to time
up to and including 5:00 p.m. (Pacific time) on the earlier of (i) the
closing of the initial public offering of the Company's Common Stock pursuant
to a registration statement under the Securities Act of 1933, as amended (the
"Initial Public Offering"), (ii) an Organic Change (as provided in Section
3.3 of this Warrant), or (iii) five (5) years from the date of this Warrant,
such earlier day being referred to herein as the "Expiration Date", upon
surrender to the Company at its principal office (or at such other location
as the Company may advise the Holder in writing) of this Warrant properly
endorsed with the Form of Subscription attached hereto duly filled in and
signed and, if applicable, upon payment in cash or by check of the aggregate
Stock Purchase Price for the number of shares for which this Warrant is being
exercised determined in accordance with the provisions hereof. The Company
shall deliver notice of the Initial Public Offering or Organic Change to the
Holder at least 20 days prior to the closing thereof. The Maximum Purchase
Amount shall be determined by multiplying (i) the principal amount loaned to
the Company pursuant to that certain Convertible Promissory Note entered into
by the Company and the Holder on even date herewith (the "Note") by (ii)
10.0%, and dividing the product of (i) and (ii) by the Stock Purchase Price.
The Stock Purchase Price and the number of shares purchasable hereunder are
subject to adjustment as provided in Section 3 of this Warrant.

         This Warrant is subject to the following terms and conditions:

         1.    EXERCISE; ISSUANCE OF CERTIFICATES; PAYMENT FOR SHARES.

               1.1 GENERAL. This Warrant is exercisable at the option of the
holder of record hereof, at any time or from time to time, up to the Expiration
Date for all or any part of the shares

                                       1.

<PAGE>

of Preferred Stock (but not for a fraction of a share) which may be purchased
hereunder. The Company agrees that the shares of Preferred Stock purchased
under this Warrant shall be and are deemed to be issued to the Holder hereof
as the record owner of such shares as of the close of business on the date on
which this Warrant shall have been surrendered, properly endorsed, the
completed, executed Form of Subscription delivered and payment made for such
shares. Certificates for the shares of Preferred Stock so purchased, together
with any other securities or property to which the Holder hereof is entitled
upon such exercise, shall be delivered to the Holder hereof by the Company at
the Company's expense within a reasonable time after the rights represented
by this Warrant have been so exercised. In case of a purchase of less than
all the shares which may be purchased under this Warrant, the Company shall
cancel this Warrant and execute and deliver a new Warrant or Warrants of like
tenor for the balance of the shares purchasable under the Warrant surrendered
upon such purchase to the Holder hereof within a reasonable time. Each stock
certificate so delivered shall be in such denominations of Preferred Stock as
may be requested by the Holder hereof and shall be registered in the name of
such Holder.

               1.2 NET ISSUE EXERCISE. Notwithstanding any provisions herein to
the contrary, if the fair market value of one share of the Company's Preferred
Stock is greater than the Stock Purchase Price (at the date of calculation as
set forth below), in lieu of exercising this Warrant for cash, the Holder may
elect to receive shares equal to the value (as determined below) of this Warrant
(or the portion thereof being canceled) by surrender of this Warrant at the
principal office of the Company together with the properly endorsed Form of
Subscription and notice of such election, in which event the Company shall issue
to the Holder a number of shares of Preferred Stock computed using the following
formula:

                           X = Y (A-B)
                               -------
                                   A

                     Where X = the  number  of  shares  of  Preferred  Stock
                               to be issued to the Holder

                           Y = the number of shares of Preferred Stock
                               purchasable under the Warrant or, if only a
                               portion of the Warrant is being exercised, the
                               portion of the Warrant being canceled (at the
                               date of such calculation)

                           A   = the fair market value of one share of the
                               Company's Preferred Stock (at the date of such
                               calculation)

                           B = Stock Purchase Price (as adjusted to the date
                               of such calculation)

For purposes of the above calculation, fair market value of one share of
Preferred Stock shall be determined by the Company's Board of Directors in good
faith; provided, however, that in the event the Company makes an initial public
offering of its Common Stock the fair market value per share shall be the
product of (i) the per share offering price to the public of the Company's
initial

                                       2.

<PAGE>

public offering, and (ii) the number of shares of Common Stock into
which each share of Preferred Stock is convertible at the time of such exercise.

         2. SHARES TO BE FULLY PAID; RESERVATION OF SHARES. The Company
covenants and agrees that all shares of Preferred Stock which may be issued
upon the exercise of the rights represented by this Warrant will, upon
issuance, be duly authorized, validly issued, fully paid and nonassessable
and free from all preemptive rights of any shareholder and free of all taxes,
liens and charges with respect to the issue thereof. The Company further
covenants and agrees that, during the period within which the rights
represented by this Warrant may be exercised, the Company will at all times
have authorized and reserved, for the purpose of issue or transfer upon
exercise of the subscription rights evidenced by this Warrant, a sufficient
number of shares of authorized but unissued Preferred Stock, or other
securities and property, when and as required to provide for the exercise of
the rights represented by this Warrant. The Company will take all such action
as may be necessary to assure that such shares of Preferred Stock may be
issued as provided herein without violation of any applicable law or
regulation, or of any requirements of any domestic securities exchange upon
which the Preferred Stock may be listed; provided, however, that the Company
shall not be required to effect a registration under Federal or State
securities laws with respect to such exercise. The Company will not take any
action which would result in any adjustment of the Stock Purchase Price (as
set forth in Section 3 hereof) (i) if the total number of shares of Preferred
Stock issuable after such action upon exercise of all outstanding warrants,
together with all shares of Preferred Stock then outstanding and all shares
of Preferred Stock then issuable upon exercise of all options and upon the
conversion of all convertible securities then outstanding, would exceed the
total number of shares of Preferred Stock then authorized by the Company's
Certificate of Incorporation, or (ii) if the total number of shares of Common
Stock issuable after such action upon the conversion of all such shares of
Preferred Stock, together with all shares of Common Stock then issuable upon
exercise of all options and upon the conversion of all such shares of
Preferred Stock, together with all shares of Common Stock then outstanding
and all shares of Common Stock then issuable upon exercise of all options and
upon the conversion of all convertible securities then outstanding would
exceed the total number of shares of Common Stock then authorized by the
Company's Certificate of Incorporation.

         3. ADJUSTMENT OF STOCK PURCHASE PRICE AND NUMBER OF SHARES. The
Stock Purchase Price and the number of shares purchasable upon the exercise
of this Warrant shall be subject to adjustment from time to time upon the
occurrence of certain events described in this Section 3. Upon each
adjustment of the Stock Purchase Price, the Holder of this Warrant shall
thereafter be entitled to purchase, at the Stock Purchase Price resulting
from such adjustment, the number of shares obtained by multiplying the Stock
Purchase Price in effect immediately prior to such adjustment by the number
of shares purchasable pursuant hereto immediately prior to such adjustment,
and dividing the product thereof by the Stock Purchase Price resulting from
such adjustment.

               3.1 SUBDIVISION OR COMBINATION OF STOCK. In case the Company
shall at any time subdivide its outstanding shares of Preferred Stock into a
greater number of shares, the

                                       3.

<PAGE>

Stock Purchase Price in effect immediately prior to such subdivision shall be
proportionately reduced, and conversely, in case the outstanding shares of
Preferred Stock of the Company shall be combined into a smaller number of
shares, the Stock Purchase Price in effect immediately prior to such
combination shall be proportionately increased.

               3.2 DIVIDENDS IN PREFERRED STOCK, OTHER STOCK, PROPERTY,
RECLASSIFICATION. If at any time or from time to time the Holders of
Preferred Stock (or any shares of stock or other securities at the time
receivable upon the exercise of this Warrant) shall have received or become
entitled to receive, without payment therefor,

                    (a) Preferred Stock or any shares of stock or other
securities which are at any time directly or indirectly convertible into or
exchangeable for Preferred Stock, or any rights or options to subscribe for,
purchase or otherwise acquire any of the foregoing by way of dividend or
other distribution,

                    (b) any cash paid or payable otherwise than as a cash
dividend, or

                    (c) Preferred Stock or additional stock or other
securities or property (including cash) by way of spinoff, split-up,
reclassification, combination of shares or similar corporate rearrangement,
(other than shares of Preferred Stock issued as a stock split or adjustments
in respect of which shall be covered by the terms of Section 3.1 above), then
and in each such case, the Holder hereof shall, upon the exercise of this
Warrant, be entitled to receive, in addition to the number of shares of
Preferred Stock receivable thereupon, and without payment of any additional
consideration therefor, the amount of stock and other securities and property
(including cash in the cases referred to in clause (b) above and this clause
(c)) which such Holder would hold on the date of such exercise had he been
the holder of record of such Preferred Stock as of the date on which holders
of Preferred Stock received or became entitled to receive such shares or all
other additional stock and other securities and property.

               3.3 REORGANIZATION, RECLASSIFICATION, CONSOLIDATION, MERGER OR
SALE. If any recapitalization, reclassification or reorganization of the
capital stock of the Company, or any consolidation or merger of the Company
with another corporation, or the sale of all or substantially all of its
assets or other transaction shall be effected in such a way that holders of
Preferred Stock shall be entitled to receive stock, securities, or other
assets or property (an "Organic Change"), then, as a condition of such
Organic Change, lawful and adequate provisions shall be made by the Company
whereby the Holder hereof shall thereafter have the right to purchase and
receive (in lieu of the shares of the Preferred Stock of the Company
immediately theretofore purchasable and receivable upon the exercise of the
rights represented hereby) such shares of stock, securities or other assets
or property as may be issued or payable with respect to or in exchange for a
number of outstanding shares of such Preferred Stock equal to the number of
shares of such stock immediately theretofore purchasable and receivable upon
the exercise of the rights represented hereby; provided, however, that in the
event the value of the stock, securities or other assets or property
(determined in good faith by the Board of Directors of the Company) issuable
or payable with respect to one share of the Preferred Stock of the Company
immediately theretofore purchasable and receivable upon the exercise of the
rights represented hereby is in

                                       4.

<PAGE>

excess of the Stock Purchase Price hereof effective at the time of a merger,
and securities received in such reorganization, if any, are publicly traded,
then this Warrant shall expire unless exercised prior to such Organic Change.
In the event of any Organic Change, appropriate provision shall be made by
the Company with respect to the rights and interests of the Holder of this
Warrant to the end that the provisions hereof (including, without limitation,
provisions for adjustments of the Stock Purchase Price and of the number of
shares purchasable and receivable upon the exercise of this Warrant) shall
thereafter be applicable, in relation to any shares of stock, securities or
assets thereafter deliverable upon the exercise hereof. The Company will not
effect any such consolidation, merger or sale unless, prior to the
consummation thereof, the successor corporation (if other than the Company)
resulting from such consolidation or the corporation purchasing such assets
shall assume by written instrument reasonably satisfactory in form and
substance to the Holders of a majority of the warrants to purchase Preferred
Stock then outstanding, executed and mailed or delivered to the registered
Holder hereof at the last address of such Holder appearing on the books of
the Company, the obligation to deliver to such Holder such shares of stock,
securities or assets as, in accordance with the foregoing provisions, such
Holder may be entitled to purchase.

               3.4 CERTAIN EVENTS. If any change in the outstanding Preferred
Stock of the Company or any other event occurs as to which the other
provisions of this Section 3 are not strictly applicable or if strictly
applicable would not fairly protect the purchase rights of the Holder of the
Warrant in accordance with such provisions, then the Board of Directors of
the Company shall make an adjustment in the number and class of shares
available under the Warrant, the Stock Purchase Price or the application of
such provisions, so as to protect such purchase rights as aforesaid. The
adjustment shall be such as will give the Holder of the Warrant upon exercise
for the same aggregate Stock Purchase Price the total number, class and kind
of shares as he would have owned had the Warrant been exercised prior to the
event and had he continued to hold such shares until after the event
requiring adjustment.

               3.5  NOTICES OF CHANGE.

                    (a)  Immediately upon any adjustment in the number or
class of shares subject to this Warrant and of the Stock Purchase Price, the
Company shall give written notice thereof to the Holder, setting forth in
reasonable detail and certifying the calculation of such adjustment.

                    (b)  The Company shall give written notice to the Holder
at least 20 business days prior to the date on which the Company closes its
books or takes a record for determining rights to receive any dividends or
distributions.

                    (c)  The Company  shall also give written  notice to the
Holder at least 20 business days prior to the date on which an Organic Change
shall take place.

     4.   ISSUE TAX. The  issuance of  certificates  for shares of  Preferred
Stock upon the exercise of the Warrant shall be made without charge to the
Holder of the Warrant for any issue tax (other than any applicable income
taxes) in respect thereof; provided, however, that the

                                       5.

<PAGE>

Company shall not be required to pay any tax which may be payable in respect
of any transfer involved in the issuance and delivery of any certificate in a
name other than that of the then Holder of the Warrant being exercised.

     5. CLOSING OF BOOKS. The Company will at no time close its transfer
books against the transfer of any warrant or of any shares of Preferred Stock
issued or issuable upon the exercise of any warrant in any manner which
interferes with the timely exercise of this Warrant.

     6. NO VOTING OR DIVIDEND RIGHTS; LIMITATION OF LIABILITY. Nothing
contained in this Warrant shall be construed as conferring upon the Holder
hereof the right to vote or to consent or to receive notice as a shareholder
of the Company or any other matters or any rights whatsoever as a shareholder
of the Company. No dividends or interest shall be payable or accrued in
respect of this Warrant or the interest represented hereby or the shares
purchasable hereunder until, and only to the extent that, this Warrant shall
have been exercised. No provisions hereof, in the absence of affirmative
action by the Holder to purchase shares of Preferred Stock, and no mere
enumeration herein of the rights or privileges of the Holder hereof, shall
give rise to any liability of such Holder for the Stock Purchase Price or as
a shareholder of the Company, whether such liability is asserted by the
Company or by its creditors.

     7. WARRANTS TRANSFERABLE. Subject to compliance with applicable federal
and state securities laws, this Warrant and all rights hereunder are
transferable, in whole or in part, without charge to the holder hereof
(except for transfer taxes), upon surrender of this Warrant properly
endorsed. Each taker and holder of this Warrant, by taking or holding the
same, consents and agrees that this Warrant, when endorsed in blank, shall be
deemed negotiable, and that the holder hereof, when this Warrant shall have
been so endorsed, may be treated by the Company, at the Company's option, and
all other persons dealing with this Warrant as the absolute owner hereof for
any purpose and as the person entitled to exercise the rights represented by
this Warrant, or to the transfer hereof on the books of the Company any
notice to the contrary notwithstanding; but until such transfer on such
books, the Company may treat the registered owner hereof as the owner for all
purposes.

     8. RIGHTS AND OBLIGATIONS SURVIVE EXERCISE OF WARRANT. The rights and
obligations of the Company, of the holder of this Warrant and of the holder
of shares of Preferred Stock issued upon exercise of this Warrant, shall
survive the exercise of this Warrant.

     9. MODIFICATION AND WAIVER. This Warrant and any provision hereof may be
changed, waived, discharged or terminated only by an instrument in writing
signed by the party against which enforcement of the same is sought.

     10. NOTICES. Any notice, request or other document required or permitted
to be given or delivered to the holder hereof or the Company shall be
delivered or shall be sent by certified mail, postage prepaid, to each such
holder at its address as shown on the books of the Company or to the Company
at the address indicated therefor in the first paragraph of this Warrant or
such other address as either may from time to time provide to the other.

                                       6.

<PAGE>

     11. BINDING EFFECT ON SUCCESSORS. This Warrant shall be binding upon any
corporation succeeding the Company by merger, consolidation or acquisition of
all or substantially all of the Company's assets. All of the obligations of
the Company relating to the Preferred Stock issuable upon the exercise of
this Warrant shall survive the exercise and termination of this Warrant. All
of the covenants and agreements of the Company shall inure to the benefit of
the successors and assigns of the holder hereof.

     12. DESCRIPTIVE HEADINGS AND GOVERNING LAW. The description headings of
the several sections and paragraphs of this Warrant are inserted for
convenience only and do not constitute a part of this Warrant. This Warrant
shall be construed and enforced in accordance with, and the rights of the
parties shall be governed by, the laws of the State of California.

     13. LOST WARRANTS. The Company represents and warrants to the Holder
hereof that upon receipt of evidence reasonably satisfactory to the Company
of the loss, theft, destruction, or mutilation of this Warrant and, in the
case of any such loss, theft or destruction, upon receipt of an indemnity
reasonably satisfactory to the Company, or in the case of any such mutilation
upon surrender and cancellation of such Warrant, the Company, at its expense,
will make and deliver a new Warrant, of like tenor, in lieu of the lost,
stolen, destroyed or mutilated Warrant.

     14. FRACTIONAL SHARES. No fractional shares shall be issued upon
exercise of this Warrant. The Company shall, in lieu of issuing any
fractional share, pay the holder entitled to such fraction a sum in cash
equal to such fraction multiplied by the then effective Stock Purchase Price.

     15. MARKET STANDOFF. The Holder of this Warrant, by acceptance hereof,
agrees that such Holder will not, without the prior written consent of the
lead underwriter of the Company's initial public offering, directly or
indirectly offer to sell, contract to sell (including, without limitation,
any short sale), grant any option for the sale of, acquire any option to
dispose of, or otherwise dispose of any shares subject to this Warrant for a
period of 180 days following the day on which the registration statement
filed on behalf of the Company in connection with the initial public offering
shall become effective by order of the Securities and Exchange Commission.

                      [THIS SPACE INTENTIONALLY LEFT BLANK]

                                       7.

<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Warrant to be duly
executed by its officers, thereunto duly authorized this 4th day of December,
1998.

                                                  RIGEL PHARMACEUTICALS, INC.
                                                  A Delaware corporation

                                                  By: _________________________

                                                  Title: ______________________

ATTEST:

______________________________________
Secretary

<PAGE>

                                    EXHIBIT A

                                SUBSCRIPTION FORM

                                                  Date: ________________, 19___

Rigel Pharmaceuticals, Inc.
772 Lucerne Drive
Sunnyvale, CA 94086

Attn:  President

Ladies and Gentlemen:

/ /      The undersigned hereby elects to exercise the warrant issued to it by
         Rigel Pharmaceuticals, Inc. (the "Company") and dated ___________
         _____, ____ Warrant No. PDW-___ (the "Warrant") and to purchase
         thereunder __________________________________ shares of the Series D
         Preferred Stock of the Company (the "Shares") at a purchase price of
         ___________________________________________ Dollars ($__________) per
         Share or an aggregate purchase price of
         __________________________________ Dollars ($__________) (the "Purchase
         Price").

/ /      The undersigned hereby elects to convert _______________________
         percent (____%) of the value of the Warrant pursuant to the provisions
         of Section 1.2 of the Warrant.

         Pursuant to the terms of the Warrant, and unless exercised pursuant
to Section 1.2 of the Warrant, the undersigned has delivered the Purchase
Price herewith in full in cash or by certified check or wire transfer.

                                              Very truly yours,

                                              _________________________________

                                              By: _____________________________

                                              Title:___________________________

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