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                            ALLOS THERAPEUTICS, INC.

            FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT

                                October 4, 1999
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                                TABLE OF CONTENTS
                                   (CONTINUED)


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                                                                                                                   PAGE
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7.       Information Rights..........................................................................................22

         7.1      Financial Information..............................................................................22
         7.2      Additional Information and Rights..................................................................23

8.       Voting and Other Covenants..................................................................................24

         8.1      Agreement to Vote..................................................................................24
         8.2      Voting Events......................................................................................24
         8.3      Designation and Election of Directors..............................................................24
         8.4      Successors in Interest.............................................................................25
         8.5      Conversion Stock...................................................................................25

9.       Miscellaneous...............................................................................................26

         9.1      Conditions to Exercise of Rights...................................................................26
         9.2      Repurchase Agreement...............................................................................26
         9.3      Governing Law......................................................................................26
         9.4      Amendment..........................................................................................26
         9.5      Assignment of Rights...............................................................................26
         9.6      Term...............................................................................................26
         9.7      Notices............................................................................................27
         9.8      Severability.......................................................................................27
         9.9      Attorney Fees......................................................................................27
         9.10     Counterparts.......................................................................................27
         9.11     Entire Agreement...................................................................................27
         9.12     Aggregation of Stock...............................................................................27
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            FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT

         This Amended and Restated Stockholder Rights Agreement (this
"Agreement") is made as of the 4th day of October, 1999 by and among Allos
Therapeutics, Inc., a Delaware corporation (the "Company") and the parties
listed on Exhibit A (the "Stockholders"). This Agreement is being executed in
conjunction with the Company's Series C Convertible Preferred Stock Purchase
Agreement of even date herewith (the "Series C Purchase Agreement").

         This Agreement amends and restates the Shareholder Rights Agreement
dated March 15, 1996, as amended (the "Prior Rights Agreement") in its entirety.
Such amendment and restatement shall be effective upon the execution of this
Agreement by (i) the Company, (ii) the holders of more than fifty percent (50%)
in interest of the Restricted Founders Shares (as defined below) outstanding
immediately prior to the execution of the Series C Purchase Agreement and (iii)
the holders of more than fifty percent (50%) in interest of the Registrable
Securities (as defined below) outstanding immediately prior to the execution of
the Series C Purchase Agreement.

         In consideration of the mutual covenants set forth herein, the parties
agree as follows:

         1. Definitions.

         1.1 "CIT" shall mean the Center for Innovative Technology, a Virginia
corporation.

         1.2 "CIT Transferees" shall mean Virginia Commonwealth University, the
Virginia Commonwealth University Intellectual Property Foundation, Donald J.
Abraham, Ahmed Mehanna, Ramnarayan Randad and Mona Mahran.

         1.3 "Commission" shall mean the Securities and Exchange Commission or
any other federal agency at the time administering the Securities Act.

         1.4 "Common Holder" shall mean any holder of outstanding Restricted
Founders Shares.

         1.5 "Common Stock" shall mean the Company's outstanding Common Stock
and shares of Common Stock issued or issuable upon conversion of the Company's
outstanding Preferred Stock from time to time.

         1.6 "Exchange Act" shall mean the Securities Exchange Act of 1934, as
amended, or any similar successor federal statute and the rules and regulations
thereunder, all as the same shall be in effect from time to time.

         1.7 "Founders" shall mean Donald J. Abraham, James B. Farinholt, Jr.
and Stephen J. Hoffman.

         1.8 "Holder" shall mean any holder of outstanding Registrable
Securities.



<PAGE>   4


         1.9 "Initiating Holders" shall mean any Holders of not less than 40% of
the outstanding Registrable Securities.

         1.10 "Preferred Holder" shall mean any holder of outstanding Restricted
Preferred Shares.

         1.11 "Preferred Stock" shall mean outstanding shares of the Company's
Series A Preferred Stock, Series B Preferred Stock and Series C Preferred Stock.

         1.12 The terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act (and any post-effective amendments filed or
required to be filed), and the declaration or ordering of the effectiveness of
such registration statement.

         1.13 "Registrable Securities" shall mean (i) any shares of Common Stock
issued or issuable, directly or indirectly, in respect of such stock upon the
conversion of the Preferred Stock which was purchased under the Series A
Preferred Stock and Warrant Purchase Agreement dated January 14, 1994, the
Series A Preferred Stock Purchase Agreement dated June 20, 1995, the Series B
Preferred Stock Purchase Agreement dated March 17, 1996, as amended by the
Amendment Agreement dated June 26, 1996, the Series C Convertible Preferred
Stock Purchase Agreement dated January 13, 1998, as amended by the Amendment
Agreement dated May 4, 1998, or the Series C Purchase Agreement and (ii) any
shares of Common Stock issued or issuable, directly or indirectly, in respect of
such Registrable Securities upon any stock split, stock dividend,
recapitalization, or similar event, or any shares of Common Stock otherwise
issued or issuable with respect to such Registrable Securities; provided,
however, that Registrable Securities shall not include any shares of Common
Stock which have previously been registered or sold to the public.

         1.14 "Registration Expenses" shall mean all expenses incurred by the
Company in complying with Sections 4. 1, 4.2 and 4.3 of this Agreement,
including, without limitation, all registration, qualification and filing fees,
printing expenses, escrow fees, fees and disbursements of counsel for the
Company and fees and disbursements of one counsel for the Holders (up to
$25,000), blue sky fees and expenses, and the expense of any special audits
incident to or required by any such registration (but excluding the compensation
of regular employees of the Company which shall be paid in any event by the
Company). Registration Expenses shall not include selling commissions, discounts
or other compensation paid to underwriters or other agents or brokers to effect
the sale.

         1.15 "Restricted Securities" shall mean the securities of the Company
required to bear the legend set forth in Section 6 of this Agreement.

         1.16 "Restricted Founders Shares" shall mean shares of Common Stock now
owned or subsequently acquired by (i) the Founders or their transferees or
assignees, including A. P. Investment Corporation and Nancy W. Abraham, Trustee,
U/A 12-14-94 (also, the "Founders"), (ii) CIT or (iii) the CIT Transferees.

         1.17 "Restricted Preferred Shares" shall mean shares of the Company's
(i) Preferred Stock and (ii) Common Stock issued or issuable upon conversion of
the Company's Preferred Stock.

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         1.18 "Rule 145" shall mean Rule 145 promulgated under the Securities
Act, or any similar successor rule, as the same shall be in effect from time to
time.

         1.19 "Rule 415" shall mean Rule 415 promulgated under the Securities
Act, or any similar successor rule, as the same shall be in effect from time to
time.

         1.20 "Selling Expenses" shall mean all underwriting discounts, selling
commissions and stock transfer taxes applicable to the sale of Registrable
Securities.

         1.21 "Securities Act" shall mean the Securities Act of 1933, as
amended, or any similar federal statute and the rules and regulations of the
Commission thereunder, as shall be in effect at the time.

         2. Right of First Refusal on Restricted Founders Shares.

         2.1 Restrictions on Transfers. Except as provided in this Agreement, no
Common Holder shall transfer or otherwise dispose of any Restricted Founders
Shares owned by such Common Holder, or any interest therein, and any attempt by
any Common Holder to effect a transfer in violation of this Section 2 shall be
void and ineffective for all purposes. The words "transfer" and "dispose"
include the making of any sale, exchange, assignment, gift, security interest,
pledge or other encumbrance, or any contract therefor, any voting trust or other
agreement or arrangement with respect to the transfer of voting rights or any
other beneficial interest in Restricted Founders Shares, the creation of any
other claim thereto or any other transfer or disposition whatsoever, whether
voluntary or involuntary, affecting the right, title, or possession with respect
to the Restricted Founders Shares.

         2.2 Third Party Offers. Each Common Holder hereby agrees that subject
to the terms and conditions set forth below, should any Common Holder (the
"Offeree Holder") receive one or more bona fide offers upon specific terms and
conditions (including a purchase price payable in cash or other property)
(collectively the "Purchase Offer"), from any persons, to purchase any
Restricted Founders Shares from such Offeree Holder, then such Offeree Holder
shall promptly notify the Preferred Holders of the terms and conditions of such
Purchase Offer (the "Notice").

         2.3 Right of First Refusal.

             (a) Each Preferred Holder shall have the right and option (subject
to the provisions of Section 2.3(c) hereof), for a period of 20 days after
receipt of the Notice, to buy all or any of its Proportionate Percentage (as
such term is defined below) of the Restricted Founders Shares so offered at the
purchase price and on the terms stated in the Purchase Offer and to offer, in
any written notice of acceptance, to purchase any of such Restricted Founders
Shares not purchased by other Preferred Holders, in which case such Restricted
Founders Shares not accepted by the other Preferred Holders shall be deemed to
have been offered to and accepted by the Preferred Holder(s) which exercised
their option under this Section 2.3(a) pro rata in accordance with their
respective Proportionate Percentages (as such term is defined below), on the
above-described terms and conditions.


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             (b) Sales of Restricted Founders Shares under the terms of Section
2.3(a) above shall be made at the offices of the Company on a mutually
satisfactory business day within 15 days after the expiration of the aforesaid
offering period. Delivery of certificates or other instruments evidencing such
Restricted Founders Shares duly endorsed for transfer to the Preferred Holders
shall be made on such date against payment of the purchase price therefor.

             (c) If effective acceptance shall not be received pursuant to
Section 2.3(a) above with respect to all Restricted Founders Shares offered for
sale pursuant to the Notice, then the Offeree Holder may, subject to the
remaining provisions of Sections 2 and 6, sell all or any part of the remaining
Restricted Founders Shares so offered for sale at a price not less than the
price, an on terms and conditions not more favorable to the purchaser thereof
than the terms and conditions, stated in the original Purchase Offer at any time
within 90 days after the expiration of the offer required by Section 2.3(a)
above. In the event the remaining Restricted Founders Shares are not sold by the
Offeree Holder during such 90-day period, the right of the Offeree Holder to
sell such remaining Restricted Founders Shares shall expire and the obligations
of this Section 2 shall be reinstated; provided, however, that in the event the
Offeree Holder determines, at any time during such 90-day period, that the sale
of all or any part of the Restricted Founders Shares on the terms set forth in
the written notice of intention to sell is impractical, the Offeree Holder may
terminate the offer and reinstate the procedure provided in this Section 2
without waiting for the expiration of such 90-day period.

             (d) The Offeree Holder may specify in the Notice that all
Restricted Founders Shares mentioned therein must be sold, in which case any
acceptance received pursuant to Section 2.3(a) hereof shall be deemed
conditioned upon (A) receipt of one or more written notices of acceptance with
respect to all Restricted Founders Shares mentioned in such Notice and/or (B)
the sale of the remaining Restricted Founders Shares, if any, pursuant to
Section 2.3(c) above.

             (e) "Proportionate Percentage" shall mean the pro rata percentage
of shares of stock being offered by an Offeree Holder pursuant to Section 2.3
hereof which each Preferred Holder shall be entitled to purchase. Such pro rata
percentage, as to each such Preferred Holder, shall be the percentage figure
which expresses the ratio between the number of shares of outstanding Common
Stock owned by such Preferred Holder and the aggregate number of shares of
Common Stock owned by all such Preferred Holders.

             (f) Anything contained herein to the contrary notwithstanding, the
Offeree Holder shall, in addition to complying with the provisions of this
Section 2.3 in the event of a proposed sale of Restricted Founders Shares,
comply with the provisions of Section 5.1 hereof.

         2.4 Exempt Transfers.

             (a) Notwithstanding the foregoing, the provisions of Sections 2 and
5 hereof shall not apply to (i) any pledge of Restricted Founders Shares made by
a Founder pursuant to a bona fide loan transaction that creates a mere security
interest; (ii) any transfer to the ancestors, descendants or spouse or to trusts
for the benefit of such persons or a Founder; or (iii) any bona fide gift by a
Founder, provided that (A) the transferring Founder shall inform the Preferred
Holders of such


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pledge, transfer or gift prior to effecting it and (B) the pledgee, transferee
or donee shall furnish the Preferred Holders with a written agreement to be
bound by and comply with all provisions of Sections 2 and 5 hereof. Such
transferred Restricted Founders Shares shall remain "Restricted Founders Shares"
hereunder, and such pledgee, transferee or donee shall be treated as a "Founder"
and "Common Holder" for purposes of this Agreement.

             (b) Notwithstanding the foregoing, the provisions of Sections 2 and
5 hereof shall not apply to any transfer by CIT to a CIT Transferee or by
Virginia Commonwealth University or the Virginia Commonwealth University
Intellectual Property Foundation to a CIT Transferee, provided that such CIT
Transferee agrees in writing to be bound by and comply with all terms and
conditions of this Agreement. Such transferred Restricted Founders Shares shall
remain "Restricted Founders Shares" hereunder and such CIT Transferee shall be
treated as a "Common Holder" for purposes of this Agreement.

             (c) Notwithstanding the foregoing, the provisions of Sections 2 and
5 shall not apply to the sale of any Restricted Founders Shares (i) to the
public pursuant to a registration statement filed with and declared effective
by, the Commission under the Securities Act; or (ii) to the Company; or (iii) if
prior to such sale, (A) the Common Holder (other than a Common Holder who is a
CIT Transferee) holds less than 2.5% of the Company's outstanding shares of
capital stock or (B) with respect to the Founders, the Founders collectively
hold less than 5.0% of the Company's outstanding shares of capital stock or (C)
with respect to the Common Holders, the Common Holders collectively hold less
than 0.5% of the Company's outstanding shares of capital stock.

         3. Right of First Offer on New Securities.

         3.1 Waiver of Right. The Holders under the Prior Rights Agreement waive
their Right of First Offer, including any notice rights pertaining thereto,
under the Prior Rights Agreement to purchase the shares of Series C Preferred
Stock being issued and sold under the Series C Purchase Agreement.

         3.2 Right of First Offer to Holders. The Company hereby grants to each
Holder the irrevocable and exclusive first option (the "First Option") to
purchase all or part of such Holders Pro Rata Portion (as defined below) of any
New Securities (as defined in Section 3.4) which the Company may, from time to
time after the date of this Agreement, propose to issue and sell. For purposes
of this Section 3, a Holder's "Pro Rata Portion" shall be equal to the product
of (i) the total number of New Securities proposed to be issued multiplied by
(ii) a fraction, the numerator of which is the number of shares of Common Stock
held by such Holder (computed as set forth in Section 3.3 hereof) as of the date
of the Company Notice provided by the Company pursuant to Section 3.5, and the
denominator of which is the total number of shares of Common Stock which are
outstanding as of such date. Furthermore, if one or more Holders do not,
pursuant to Section 3.5, give notice of its or their intention to exercise in
full its or their option to purchase its or their Pro Rata Portion of the New
Securities, then each Holder who did give notice of such intent (collectively,
the "Fully Participating Holders") shall have the irrevocable and exclusive
second option (the "Second Option") to purchase all or a part of the New
Securities as to which a notice pursuant to the exercise of the First Option
could have been, but was not, delivered (for purposes of this Section 3, the
"Additional


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New Securities"). If more than one Fully Participating Holder gives a notice (a
"Second Notice") pursuant to Section 3.5 of its intention to purchase Additional
New Securities pursuant to the exercise of the Second Option and the total
number of New Securities covered by such notices exceeds the total number of
Additional New Securities, then the Additional New Securities shall be allocated
among such Fully Participating Holders according to the following procedure, or
in such different proportions as such Fully Participating Holders shall agree
among themselves:

             (a) Each Oversubscribing Holder (as defined below) shall be
apportioned the lesser of (A) that number of Additional New Securities that it
elected to purchase in its Second Notice and which it has not yet been
apportioned pursuant to this Section 3.2(a); or (B) its Pro Rata Portion of the
Additional New Securities (as defined below);

             (b) If the apportionment in Section 3.2(a) is followed and there
remain (A) at least one Oversubscribing Holder who has not yet been apportioned
the number of Additional New Securities it elected to purchase in its Second
Notice and (B) any Additional New Securities, then the procedure described in
Section 3.2(a) shall be repeated; and

             (c) For purposes of this Section 3.2, an "Oversubscribing Holder"
means a Fully Participating Holder who has given a Second Notice and who has not
yet been apportioned pursuant to Section 3.2(a) that number of Additional New
Securities that it elected to purchase in its Second Notice, and an
Oversubscribing Holder's "Pro Rata Portion of Additional New Securities" shall
be equal to the number of Additional New Securities multiplied by a fraction,
the numerator of which is the number of shares of Common Stock held by such
Holder as of the date of the Company Notice, and the denominator of which is the
total number of shares of Common Stock held by all Oversubscribing Holders as of
such date.

         3.3 Calculation of Number of Shares of Common Stock Held or
Outstanding. For purposes of any calculation of the number of shares of Common
Stock held or outstanding under this Section 3, and with respect to any
numerator or denominator provided herein, the conversion of all securities
convertible into or exchangeable for Common Stock and the exercise of all
outstanding options other than (i) options granted under this Section 3 and (ii)
options granted pursuant to the Company's 1995 Stock Option Plan shall be
assumed.

         3.4 "New Securities. " Except as set forth below, "New Securities"
shall mean any shares of capital stock or other equity securities (or debt
securities convertible into such equity securities) of the Company, whether now
authorized or not, and rights, options or warrants to purchase said shares of
capital stock and securities of any type whatsoever that are, or may become,
convertible into said shares of capital stock or other equity securities.
Notwithstanding the foregoing, "New Securities" shall not include:

             (a) securities issued upon conversion or exercise of the Preferred
Stock;

             (b) securities purchased or issued pursuant to the Series C
Purchase Agreement;

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             (c) securities issued pursuant to the acquisition of another
corporation by the Company by merger, purchase of all or substantially all of
the assets or other reorganization whereby the Company or its stockholders
immediately prior to such transaction continue to own more than fifty percent
(50%) of the voting power of the surviving or successor corporation;

             (d) securities issued pursuant to any rights or agreements,
including without limitation convertible securities, options and warrants,
provided that unless otherwise provided herein, the rights of first offer
established by this Section 3 shall apply with respect to the initial sale or
grant by the Company of such rights or agreements;

             (e) securities issued in connection with any stock split, stock
dividend or recapitalization by the Company;

             (f) securities issued to employees, consultants, officers or
directors of the Company pursuant to any stock option, stock purchase or stock
bonus plan, agreement or arrangement approved by the Board of Directors, but not
exceeding 3,650,000 shares of Common Stock (net of purchases of such shares or
cancellations or expirations of options);

             (g) securities issued to vendors or customers or to other persons
in similar commercial situations with the Company if such issuance is approved
by the Company's board of directors;

             (h) securities issued in connection with obtaining lease financing,
whether issued to a lessor, guarantor or other person; and

             (i) securities issued in a firm commitment underwritten public
offering pursuant to an effective registration statement under the Securities
Act, covering the offer and sale of securities for the account of the Company
and/or selling stockholders to the public at such per share price and resulting
in such aggregate net proceeds to the Company and/or the selling stockholders
(after deducting underwriters' discounts and expenses relating to the issuance)
as would result in the automatic conversion of the Company's Preferred Stock
pursuant to the Company's Amended and Restated Certificate of Incorporation.

         3.5 Notices With Respect to Proposed Issuance of New Securities. In the
event the Company proposes to undertake an issuance of New Securities, it shall
give each Holder entitled to a right of first offer pursuant to this Section 3
written notice (the "Company Notice") of its intention, describing in detail the
type of New Securities and the price and terms upon which the Company proposes
to issue such New Securities. Each such Holder shall have twenty (20) days from
the date of receipt of any such Company Notice to agree to purchase, pursuant to
the exercise of the First Option, up to such Holder's Pro Rata Portion of such
New Securities for the price and upon the terms and conditions specified in the
Company Notice by giving written notice to the Company and stating therein the
quantity of New Securities to be purchased. If, following the expiration of such
twenty (20) day period, there exist Additional New Securities subject to the
Second Option, then the Company shall give each Fully Participating Holder a
second written notice (the "Second Company Notice") to such effect and each such
Holder shall then have fifteen (15) days from the date of


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receipt of such Second Company Notice to agree to purchase (on the aforesaid
terms and conditions) the quantity of Additional New Securities stated therein,
subject to the application of the procedures set forth in Section 3.2.

         3.6 Company's Right to Complete Proposed Sale of New Securities to the
Extent Rights of First Offer are Not Exercised. In the event a Holder fails to
exercise a right of first offer with respect to any New Securities within the
periods specified in Section 3.5, the Company shall have sixty (60) days
thereafter to sell or enter into an agreement (pursuant to which the sale of
such New Securities shall be closed, if at all, within thirty (30) days from the
date of said agreement) to sell the New Securities not elected to be purchased
by Holders at the price and upon terms no more favorable to the purchasers of
such securities than those specified in the Company Notice. In the event the
Company has not sold the New Securities or entered into an agreement to sell the
New Securities within said 60 day period (or sold and issued New Securities in
accordance with the foregoing within 30 days from the date of said agreement),
the Company shall not thereafter issue or sell such New Securities without first
offering such securities in the manner provided in this Section 3 above.

         3.7 Assignment of Right of First Offer. The right of first offer
granted under this Section 3 may be assigned to a transferee or assignee in
connection with any transfer or assignment of Registrable Securities by a
Holder, provided that (a) such transfer or assignment may otherwise be effected
in accordance with applicable securities laws and (b) such transferee or
assignee acquires at least 200,000 shares of Registrable Securities (as adjusted
for combinations, stock dividends and the like) upon consummation of such
transfer or assignment.

         3.8 Amendment of Right of First Offer. Notwithstanding the provisions
of Section 9.4 hereof, the written consent of (a) the Company and (b) Holders
holding more than sixty percent (60%) in interest of the Registrable Securities
which are issued or issuable in respect of Series A Preferred Stock of the
Company and (c) Holders holding more than sixty percent (60%) in interest of the
Registrable Securities which are issued or issuable in respect of Series B
Preferred Stock of the Company and (d) Holders holding more than sixty percent
(60%) in interest of the Registrable Securities which are issued or issuable in
respect of Series C Preferred Stock of the Company shall be required to amend
Section 3.4(f) hereof to increase the number of shares of Common Stock excluded
thereby from the definition of New Securities.

         4. Registration Rights.

         4.1 Requested Registration.

             (a) Request for Registration. In case the Company shall receive
from Initiating Holders a written request that the Company effect any
underwritten registration, qualification, or compliance with respect to
Registrable Securities held by such Initiating Holders, then the Company shall:

                 (i) promptly give written notice of the proposed registration,
qualification, or compliance to all other Holders; and


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<PAGE>   11


                 (ii) as soon as practicable, use its most diligent efforts to
effect all such registration, qualification, or compliance (including, without
limitation, the execution of an undertaking to file post-effective amendments,
appropriate qualification under applicable blue sky or other state securities
laws, and appropriate compliance with applicable regulations issued under the
Securities Act and any other governmental requirements or regulations) as may be
so requested and as would permit or facilitate the sale and distribution of all
or such portion of such Registrable Securities as are specified in such request,
together with all or such portion of the Registrable Securities of any Holders
joining in such request as are specified in a written request received by the
Company, within 20 days after the date the Company mails such written notice;

         Provided, however, that the Company shall not be obligated to take any
action to effect any such registration, qualification, or compliance pursuant to
this Section 4.1:

             (A) In any jurisdiction in which the Company would be required to
execute a general consent to service of process in effecting such registration,
qualification, or compliance unless the Company is already subject to service in
such jurisdiction and except as may be required by the Securities Act;

             (B) During the period starting with the date sixty (60) days prior
to the Company's estimated date of filing of, and ending on the date one hundred
eighty (180) days immediately following the effective date of any registration
statement pertaining to securities of the Company (other than a registration of
securities in a Rule 145 transaction or with respect to an employee benefit plan
or initiated by security holders); or

             (C) Unless the aggregate offering price thereof, net of
underwriting discounts and commissions, would be at least $5,000,000;

             (D) After the Company has effected two (2) such registrations
pursuant to this Section 4.1 which have been declared or ordered effective and
pursuant to which securities have been sold.

         Subject to the foregoing clauses (A) through (D), the Company shall
file a registration statement covering the Registrable Securities so requested
to be registered as soon as practicable, and in any event within 120 days, after
receipt of the request of the Initiating Holders; provided, however, that if the
Company shall furnish to such Holder a certificate signed by the president of
the Company stating that in the good faith judgment of the board of directors of
the Company, it would be seriously detrimental to the Company or its
stockholders for such registration statement to be filed on or before the date
filing would be required and it is therefore essential to defer the filing of
such registration statement, the Company shall have the right to defer such
filing for a reasonable period not to exceed 120 days; provided, however, that
the Company shall not utilize this right more than once in any twelve-month
period.

             (b) Underwriting. The right of any Holder to registration pursuant
to this Section 4.1 shall be conditioned upon such Holder's participation in
such underwriting and the inclusion of such Holder's Registrable Securities in
the underwriting to the extent requested (unless


                                      -9-
<PAGE>   12


otherwise mutually agreed by a majority in interest of the Initiating Holders
and such Holder with respect to such participation and inclusion) to the extent
provided herein.

         The Company shall (together with all Holders selling Registrable
Securities) enter into an underwriting agreement in customary form with the
managing underwriter selected for such underwriting by a majority in interest of
the Initiating Holders. Notwithstanding any other provision of this Section 4.1,
if the managing underwriter advises the Initiating Holders in writing that
marketing factors require a limitation of the number of shares to be
underwritten, then the Company shall so advise all Holders and the number of
shares of Registrable Securities and other securities that may be included in
the registration and underwriting shall be allocated among all Holders thereof
in proportion, as nearly as practicable, to the respective amounts of securities
entitled to inclusion (determined without regard to any requirement of a request
to be included in such registration) in such registration held by all such
Holders at the time of filing the registration statement. No Registrable
Securities or other securities excluded from the underwriting by reason of the
underwriter's marketing limitation shall be included in such registration. To
facilitate the allocation of shares in accordance with the above provisions, the
Company and the underwriters may round the number of shares allocated to any
Holder to the nearest 100 shares.

         If any Holder of Registrable Securities disapproves of the terms of the
underwriting, such person may elect to withdraw therefrom by written notice to
the Company, the managing underwriter and the Initiating Holders. The
Registrable Securities and/or other securities so withdrawn shall also be
withdrawn from registration, and such Registrable Securities shall not be
transferred in a public distribution prior to 90 days after the effective date
of such registration, or such other shorter period of time as the underwriters
may require. If by the withdrawal of such Registrable Securities a greater
number of Registrable Securities held by other Holders may be included in such
registration (up to the maximum of any limitation imposed by the underwriters),
then the Company shall offer to all Holders who have included Registrable
Securities in the registration the right to include additional Registrable
Securities in the same proportion and manner used in determining the underwriter
limitation in this Section 4.1.

         If the managing underwriter has not limited the number of Registrable
Securities to be underwritten, the Company may include securities for its own
account or for the account of others in such registration if the managing
underwriter so agrees and if the number of Registrable Securities which would
otherwise have been included in such registration and underwriting will not
thereby be limited.

         4.2 Company Registration.

             (a) Notice of Registration. If at any time or from time to time,
the Company shall determine to register in an underwritten offering any of its
securities, either for its own account or the account of a security holder or
holders, other than (i) a registration relating solely to employee benefit
plans, or (ii) a registration relating solely to a Rule 145 transaction, or a
registration on any registration form that does not permit secondary sales, the
Company shall:

                 (i) promptly give to each Holder written notice thereof; and

                                      -10-
<PAGE>   13


                   (ii) include in such registration (and any related
qualification under blue sky laws or other compliance), and in any underwriting
involved therein, all the Registrable Securities specified in a written request
by each Holder received by the Company within 20 days after the Company mails
such written notice, subject to the provisions below.

             (b) Underwriting. The right of any Holder to registration pursuant
to this Section 4.2 shall be conditioned upon the participation by such Holder
in such underwriting and the inclusion of the Registrable Securities of such
Holder in the underwriting to the extent provided herein. All Holders proposing
to distribute their securities through such underwriting shall (together with
the Company and the other holders distributing their securities through such
underwriting) enter into an underwriting agreement in customary form with the
managing underwriter selected for such underwriting by the Company.
Notwithstanding any other provisions of this Section 4.2, if the managing
underwriter determines that marketing factors require a limitation of the number
of shares to be underwritten, the managing underwriter may limit the Registrable
Securities held by Holders to be included in such registration, but shall not
limit such Registrable Securities to fewer than 20% of the securities sold in
any offering; provided that in the Company's initial public offering the
managing underwriter may limit the Registrable Securities held by the Holders to
be included in such registration to fewer than 20% of the shares sold in the
offering. The Company shall so advise all Holders and the other holders
distributing their securities through such underwriting, and the number of
shares of Registrable Securities and other securities that may be included in
the registration and underwriting shall be allocated among all Holders and other
holders thereof in proportion, as nearly as practicable, to the respective
amounts of securities entitled to inclusion (determined without regard to any
requirement of a request to be included in such registration) in such
registration held by all such Holders and other holders at the time of filing
the registration statement, provided that no such inclusion of Registrable
Securities and other securities by the underwriter may reduce the securities
being offered by the Company for its own account. To facilitate the allocation
of shares in accordance with the above provisions, the Company may round the
number of shares allocated to any Holder or holder to the nearest 100 shares. If
any Holder disapproves of the terms of any such underwriting, he may elect to
withdraw therefrom by written notice to the Company and the managing
underwriter. Any securities excluded or withdrawn from such underwriting shall
be withdrawn from such registration, and shall not be transferred in a public
distribution prior to 180 days after the effective date of the registration
statement relating thereto or such other shorter period of time as the
underwriter may require.

             (c) Right to Terminate Registration. The Company shall have the
right to terminate or withdraw any registration initiated by it under this
Section 4.2 prior to the effectiveness of such registration whether or not any
Holder has elected to include securities in such registration.

         4.3 Form S-3 Registration. After its initial public offering, the
Company shall use its best efforts to qualify for registration on Form S-3 or
any comparable or successor form or forms. After the Company has qualified for
the use of Form S-3, in addition to the rights contained in the foregoing
provisions of this Section 4, the Holders of Registrable Securities shall have
the right to request registrations on Form S-3 (such requests shall be in
writing and shall state the number of shares of Registrable Securities to be
disposed of and the intended methods of disposition of such


                                      -11-
<PAGE>   14


shares by such Holder or Holders). In case the Company shall receive from a
Holder or Holders a written request that the Company effect a registration on
Form S-3 and any related qualification or compliance with respect to Registrable
Securities owned by such Holder or Holders, the Company shall:

             (a) promptly give written notice of the proposed registration, and
any related qualification or compliance, to all other Holders; and

             (b) as soon as practicable, effect such registration and all such
qualifications and compliances as may be so requested and as would permit or
facilitate the sale and distribution of all or such portion of such Holder's or
Holders' Registrable Securities as are specified in such request together with
all or such portion of the Registrable Securities or any other Holder of Holders
joining in such request as are specified in a written request given within 20
days after receipt of such written notice from the Company; provided, however,
that the Company shall not be obligated to effect any such registration,
qualification, or compliance pursuant to this Section 4.3: (i) if Form S-3 is
not available for such offering by the Holders; (ii) if the Company shall
furnish to the Holders a certificate signed by the president of the Company
stating that in the good faith judgment of the board of directors of the
Company, it would be seriously detrimental to the Company and its stockholders
for such Form S-3 registration to be effected at such time, in which event the
Company shall have the right to defer the filing of the Form S-3 registration
statement for a period of not more than 120 days after receipt of the initiating
request of the Holder or Holders under this Section 4.3; provided, however, that
the Company shall not utilize this right more than once in any twelve-month
period; (iii) if the Company has, within the six-month period preceding the date
of such request, already effected a registration on Form S-3 for any Holders
pursuant to this Section 4.3 or already effected a total of four (4)
registrations on Form S-3 pursuant to this Section 4.3; (iv) if the anticipated
aggregate offering price of the Registrable Securities to be included in such
registration, net of underwriting discounts and commissions, would be less than
$1,000,000; or (v) in any jurisdiction in which the Company would be required to
execute a general consent to service of process in effecting such registration,
qualification or compliance unless the Company is already subject to service in
such jurisdiction and except as may be required by the Securities Act.

         Subject to the foregoing, the Company shall effect such registration,
qualification, or compliance (including, without limitation, the execution of an
undertaking to file post-effective amendments, appropriate qualification under
applicable blue sky or other state securities laws and appropriate compliance
with applicable regulations issued under the Securities Act and any other
governmental requirements or regulations) covering the Registrable Securities
and other securities so requested to be registered as soon as practicable after
receipt of the request or requests of the Holder. Registrations effected
pursuant to this Section 4.3 shall not be counted as demands for registration or
registrations effected pursuant to Sections 4.1 or 4.2.

         If the registration to be effected pursuant to this Section 4.3 is to
be an underwritten public offering, it shall be managed by an underwriter or
underwriters acceptable to Company selected by a majority in interest of the
Holders requesting registration. In such event, the right of any Holder to
registration pursuant to Section 4.3 shall be conditioned upon the participation
by such


                                      -12-
<PAGE>   15


Holder in such underwriting and the inclusion of the Registrable Securities of
such Holder in the underwriting to the extent provided herein. It the managing
underwriter so selected determines that marketing factors require a limitation
of the number of shares to be underwritten, the managing underwriter may limit
the Registrable Securities held by such Holders to be included in such
registration. The Company shall so advise such Holders, and the number of shares
of Registrable Securities that may be included in the registration shall be
allocated among such Holders in proportion to the respective amounts of
Registrable Securities which would be held by each of such Holders at the time
of filing of the registration statement. Any Registrable Securities that are so
excluded from the underwriting shall be excluded from the registration. As used
throughout this Section the term "Form S-3" shall be deemed to include any
equivalent successor form for registration pursuant to the Act.

         4.4 Expenses of Registration. All Registration Expenses incurred in
connection with the registration, qualification or compliance pursuant to
Sections 4.1, 4.2 and 4.3 shall be borne by the Company; provided, however, that
the Company shall not be required to pay for expenses of any registration
proceeding begun pursuant to Section 4.1, the request of which has been
subsequently withdrawn by the Initiating Holders, in which case such expenses
shall be borne by the Holders of securities (including Registrable Securities)
pro rata in accordance with the number of shares initially sought to be
registered requesting or causing such withdrawal. All Selling Expenses relating
to securities so registered shall be borne by the holders of such securities pro
rata on the basis of the number of shares of securities so registered on their
behalf.

         4.5 Registration Procedures. If and whenever the Company is required by
the provisions of this Section 4 to use its most diligent efforts to effect
promptly the registration of Registrable Securities, the Company shall:

             (a) Prepare and file with the Commission a registration statement
with respect to such Registrable Securities and use its most diligent efforts to
cause such registration statement to become and remain effective as provided
herein.

             (b) Prepare and file with the Commission such amendments and
supplements to such registration statement and the prospectus used in connection
therewith as may be necessary to keep such registration statement effective and
current and to comply with the provisions of the Securities Act with respect to
the sale of or other disposition of all Registrable Securities covered by such
registration statement, including such amendments and supplements as may be
necessary to reflect the intended method of disposition of the prospective
seller or sellers of such Registrable Securities, but for no longer than one
hundred eighty (180) days subsequent to the effective date of such registration
in the case of a registration statement on Form S-1 (or any similar form of
registration statement required to set forth substantially identical
information) and for no longer than one hundred twenty (120) days in the case of
a registration statement on Form S-3; provided, however, that (i) such period
shall be extended for a period of time equal to the period the Holder refrains
from selling any securities included in such registration at the request of an
underwriter of Common Stock (or other securities) of the Company; and (ii) in
the case of any registration of Registrable Securities on Form S-3 which are
intended to be offered on a continuous or delayed


                                      -13-
<PAGE>   16


basis, such period shall be extended, if necessary, to keep the registration
statement effective until all such Registrable Securities are sold, provided
that Rule 415 permits an offering on a continuous or delayed basis, and provided
further that applicable rules under the Securities Act governing the obligation
to file a post-effective amendment permit, in lieu of filing a post-effective
amendment that (I) includes any prospectus required by Section 10(a)(3) of the
Securities Act or (II) reflects facts or events representing a material or
fundamental change in the information set forth in the registration statement,
the incorporation by reference of information required to be included in (I) and
(II) above to be contained in periodic reports filed pursuant to Section 13 or
15(d) of the Exchange Act in the registration statement.

             (c) Furnish to each prospective seller of Registrable Securities
such number of copies of a prospectus, including a preliminary prospectus, in
conformity with the requirements of the Securities Act, and such other
documents, as such seller may reasonably request in order to facilitate the
public sale or other disposition of the Registrable Securities of such seller.

             (d) Notify each seller of Registrable Securities covered by such
registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading or incomplete in the light of the
circumstances then existing, and at the request of any such seller, prepare and
furnish to such seller a reasonable number of copies of a supplement to or an
amendment of such prospectus as may be necessary so that, as thereafter
delivered to the purchasers of such shares, such prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading or
incomplete in the light of the circumstances then existing.

             (e) Cause all such Registrable Securities registered pursuant
hereunder to be listed on each securities exchange or approved for quotation on
any inter-dealer quotation system on which similar securities issued by the
Company are then listed or quoted.

             (f) Provide a transfer agent and registrar for all Registrable
Securities registered pursuant to such registration statement and a CUSIP number
of all such Registrable Securities, in each case not later than the effective
date of such registration.

             (g) Otherwise use its best efforts to comply with all applicable
rules and regulations of the Commission, and make available to its security
holders, as soon as reasonably practicable, an earnings statement covering the
period of at least twelve months, but not more than eighteen months, beginning
with the first month after the effective date of the registration statement,
which earnings statement shall satisfy the provisions of Section 11(a) of the
Securities Act.

             (h) In connection with any underwritten offering pursuant to a
registration statement filed pursuant to Section 4.1 hereof, the Company will
enter into an underwriting agreement reasonably necessary to effect the offer
and sale of Common Stock, provided such


                                      -14-
<PAGE>   17


underwriting agreement contains customary underwriting provisions and provided
further that if the underwriter so requests the underwriting agreement will
contain customary contribution provisions.

         4.6 Indemnification. In the event any of the Registrable Securities are
included in a registration statement under this Section 4:

             (a) The Company will indemnify each Holder, each of its officers
and directors and partners and such Holder's separate legal counsel and
independent accountants, and each person controlling such Holder within the
meaning of Section 15 of the Securities Act; and each underwriter, if any, and
each person who controls any underwriter within the meaning of Section 15 of the
Securities Act, against all expenses, claims, losses, damages or liabilities (or
actions in respect thereof), including any of the foregoing incurred in
settlement of any litigation, commenced or threatened, arising out of or based
on any untrue statement (or alleged untrue statement) of a material fact
contained, on the effective date thereof, in any registration statement, any
prospectus contained therein, or any amendment or supplement thereto, or based
on any omission (or alleged omission) to state therein a material fact required
to be stated therein or necessary to make the statements therein (in the case of
a prospectus, in the light of the circumstances under which they were made) not
misleading, or any violation by the Company of any rule or regulation
promulgated under the Securities Act applicable to the Company in connection
with any such registration, qualification or compliance, and the Company will
reimburse each such Holder, each of its officers and directors and partners and
such Holders' separate legal counsel and independent accountants and each person
controlling such Holder, each such underwriter and each person who controls any
such underwriter, for any legal and any other expenses reasonably incurred in
connection with investigating, preparing or defending any such claim, loss,
damage, liability or action, provided that the Company will not be liable in any
such case to the extent that any such claim, loss, damage, liability or expense
arises out of or is based on any untrue statement or omission or alleged untrue
statement or omission, made in reliance upon and in conformity with written
information furnished to the Company by an instrument duly executed by such
Holder or underwriter and stated to be specifically for use therein.

             (b) Each Holder, severally and not jointly, will, if Registrable
Securities held by such Holder are included in the securities as to which such
registration, qualification or compliance is being effected, indemnify the
Company, each of its directors and officers and its legal counsel and
independent accountants, each underwriter, if any, of the Company's securities
covered by such a registration statement, each person who controls the Company
or such underwriter within the meaning of Section 15 of the Securities Act; and
each other such Holder, each of its officers and directors and each person
controlling such Holder within the meaning of Section 15 of the Securities Act,
against all claims, losses, damages and liabilities (or actions in respect
thereof) arising out of or based on any untrue statement (or alleged untrue
statement) of a material fact contained, on the effective date thereof, in any
such registration statement; any prospectus contained therein, or any omission
(or alleged omission) to state therein a material fact required to be stated
therein or necessary to make the statements therein (in the case of a
prospectus, in the light of the circumstances under which they were made) not
misleading, and will reimburse the Company, such Holders, such directors,
officers, persons, underwriters or control persons for any legal or any other


                                      -15-
<PAGE>   18


expenses reasonably incurred in connection with investigating or defending any
such claim, loss, damage, liability or action, in each case to the extent, but
only to the extent, that such untrue statement (or alleged untrue statement) or
omission (or alleged omission) is made in such registration statement or
prospectus in reliance upon and in conformity with written information furnished
to the Company by an instrument duly executed by such Holder and stated to be
specifically for use therein; provided, however, that the obligations of such
Holders hereunder shall be limited to an amount equal to the net proceeds to
each such Holder of Registrable Securities sold as contemplated herein.

             (c) Each party entitled to indemnification under this Section (the
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not unreasonably be
withheld), and the Indemnified Party may participate in such defense at such
party's expense, and provided further that the failure of any Indemnified Party
to give notice as provided herein shall not relieve the Indemnifying Party of
its obligations under this Section 4.6 to the extent such failure is not
prejudicial. No Indemnifying Party, in the defense of any such claim or
litigation, shall, except with the consent of each Indemnified Party, consent to
entry of any judgment or enter into any settlement which does not include as an
unconditional term thereof the giving by the claimant or plaintiff to such
Indemnified Party of a release from all liability in respect to such claim or
litigation.

             (d) If the indemnification provided for in this Section is held by
a court of competent jurisdiction to be unavailable to an Indemnified Party with
respect to any loss, liability, claim, damage or expense referred to herein,
then the Indemnifying Party, in lieu of indemnifying the Indemnified Party,
shall contribute to the amount paid or payable by such Indemnified Party with
respect to such loss, liability, claim, damage or expense in the proportion that
is appropriate to reflect the relative fault of the Indemnifying Party and the
Indemnified Party in connection with the statements or omissions that resulted
in such loss, liability, claim, damage or expense, as well as any other relevant
equitable considerations. The relative fault of the Indemnifying Party and the
Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of material fact or the omission
(or alleged omission) to state a material fact relates to information supplied
by the Indemnifying Party or by the Indemnified Party, and the parties' relative
intent; knowledge, access to information and opportunity to correct or prevent
such statement or omission.

         4.7 Information by Holder. The Holder or Holders of Registrable
Securities included in any registration shall furnish to the Company such
information regarding such Holder or Holders and the distribution proposed by
such Holder or Holders as the Company may reasonably request in writing and as
shall be required in connection with any registration, qualification or
compliance referred to in this Section.

                                      -16-
<PAGE>   19


         4.8 Rule 144 Reporting. With a view to making available the benefits of
certain rules and regulations of the Commission which may at any time permit the
sale of the Restricted Securities to the public without registration, after such
time as a public market exists for the Common Stock of the Company, the Company
shall use its best efforts to:

             (a) Make and keep public information available, as those terms are
understood and defined in Rule 144 under the Securities Act, beginning 90 days
after (i) the effective date of the first registration statement filed by the
Company for an offering of its securities to the general public, (ii) the
Company registers a class of securities under Section 12 of the Exchange Act, or
(iii) the Company issues an offering circular meeting the requirements of
Regulation A under the Securities Act;

             (b) File with the Commission in a timely manner all reports and
other documents required of the Company under the Securities Act and the
Exchange Act (at any time after it has become subject to such reporting
requirements);

             (c) Furnish to any Holder promptly upon request a written statement
as to its compliance with the reporting requirements of Rule 144 (at any time
after 90 days after the effective date of the first registration statement filed
by the Company for an offering of its securities to the general public), and of
the Securities Act and the Exchange Act (at any time after it has become subject
to such reporting requirements), a copy of the most recent annual or quarterly
report of the Company, and such other reports and documents of the Company and
other information in the possession of or reasonably obtainable by the Company
as a Holder may reasonably request in availing itself of any rule or regulation
of the Commission allowing a Holder to sell any such securities without
registration.

         4.9 Assignment of Registration Rights. The rights to cause the Company
to register securities granted under this Section 4 may be assigned to a
transferee or assignee in connection with the transfer or assignment of shares
of Registrable Securities only if (i) such shares represent at least 1% of the
outstanding shares of the Company's capital stock (assuming conversion of all
issued and outstanding shares of Preferred Shares to Common Stock) on the date
of such assignment, or (ii) the transfer of such shares occurs in a distribution
from a Purchaser which is a partnership to a partner thereof.

         4.10 Grant of Additional Registration Rights. The Company will not
grant registration rights which are superior to or on parity with the
registration rights granted under this Agreement without the written consent of
the holders of a majority of the Registrable Securities.

         4.11 Amendment of Registration Rights. The registration rights provided
in this Section may be amended with the written consent of the Company and the
holders of a majority of the Registrable Securities. Any amendment effected in
accordance with this Section 4.11 shall be binding upon each Holder and the
Company.


                                      -17-
<PAGE>   20


      5. Right of Co-Sale and Prohibited Transfers.

         5.1 Right of Co-Sale. In the event that (x) the Preferred Holders do
not purchase pursuant to Section 2.3(a) all of the Restricted Founders Shares
which an Offeree Holder proposed to sell, assign or transfer, and (y) the
Purchase Offer will result in (1) the transfer of 25,000 or more shares of
Common Stock by such Offeree Holder or (2) the transferee of such shares holding
more than 50% of the Common Stock, each of the Preferred Holders shall have the
right, exercisable upon written notice to the Offeree Holder within 30 business
days after receipt of the Notice of the Purchase Offer, to participate in the
Offeree Holder's sale of Restricted Founders Shares pursuant to the specified
terms and conditions of such Purchase Offer. To the extent one or more of the
Preferred Holders exercise such right of participation, in accordance with the
terms and conditions hereof, the number of shares of Restricted Founders Shares
which the Offeree Holder may sell pursuant to such Purchase Offer shall be
correspondingly reduced. The right of participation of each of the Preferred
Holders shall be subject to the following terms and conditions:

             (a) Each of the Preferred Holders may sell all or any part of that
number of shares of Common Stock equal to the product obtained by multiplying
(1) the aggregate number of shares of Restricted Founders Shares covered by the
Purchase Offer by (2) a fraction, the numerator of which is the number of shares
of Common Stock at the time owned by such Preferred Holder computed in
accordance with Section 5.1(g) below) and the denominator of which is the
aggregate number of shares of Common Stock (computed in accordance with Section
5.1(g) below) at the time owned by the Common Holders and the Preferred Holders.

             (b) To the extent that any Preferred Holder fails to elect to fully
participate in such sale pursuant to subparagraph (a) above, the Offeree Holder
shall give written notice of such failure to the Preferred Holders who did so
elect (the "Participants") within five (5) days after such failure. The
Participants shall have five (5) days from the date such notice was given to
agree to sell their pro rata share of the unsold portion. For purposes of this
paragraph, a Participant's pro rata share shall be equal to the product obtained
by multiplying (1) the number of shares in the unsold portion by (2) a fraction
the numerator of which is the number of shares of Common Stock held by such
Participant (computed in accordance with Section 5.1(g) below) and the
denominator of which is the total number of shares of Common Stock held by the
Participants and the Offeree Holder (computed in accordance with Section 5.1(g)
below).

             (c) Each Participant shall effect its participation in the sale by
promptly delivering to the Offeree Holder for transfer to the prospective
purchaser one or more certificates, properly endorsed for transfer, which
represent:

                 (i) the type and number of shares of Common Stock which such
Participant elects to sell; or

                 (ii) that number of convertible securities of the Company,
which is at such time convertible into the number of shares of Common Stock
which such Participant elects to sell; provided, however, that if the
prospective purchaser objects to the delivery of convertible securities of the
Company in lieu of Common Stock, such Participant shall convert such convertible
securities


                                      -18-
<PAGE>   21


into Common Stock and deliver Common Stock as provided in subparagraph (i)
above. The Company agrees to make any such conversion concurrent with the actual
transfer of such shares to the purchaser.

             (d) The stock certificate or certificates that the Participant
delivers to the Offeree Holder pursuant to Section 5.1(c) above shall be
transferred to the prospective purchaser in consummation of the sale of
Restricted Founders Shares pursuant to the terms and conditions specified in the
Notice, and the Offeree Holder shall concurrently therewith remit to such
Participant that portion of the sale proceeds to which such Participant is
entitled by reason of its participation in such sale. To the extent that any
prospective purchaser or purchasers prohibits such assignment or otherwise
refuses to purchase shares or other securities from a Participant exercising its
right of co-sale hereunder, the Offeree Holder shall not sell to such
prospective purchaser or purchasers any Restricted Founders Shares unless and
until, simultaneously with such sale, the Offeree Holder shall purchase such
number of shares of Common Stock or other securities which each Participant
would have been able to sell under Section 5.1(a) from such Participant.

             (e) The exercise or non-exercise of the rights of the Participants
hereunder to participate in one or more sales of Restricted Founders Shares made
by the Offeree Holders shall not adversely affect their rights to participate in
subsequent sales of Restricted Founders Shares subject to this Section 5.1.

             (f) If none of the Preferred Holders elects to participate in the
sale of the Restricted Founders Shares subject to the Notice, the Offeree Holder
may, not later than sixty (60) days following delivery to the Company and each
of the Preferred Holders of the Notice, enter into an agreement providing for
the closing of the transfer of the Restricted Founders Shares covered by the
Notice within thirty (30) days of such agreement on terms and conditions not
more favorable than those described in the Notice. Any subsequent proposed
transfer of any of the Restricted Founders Shares by the Offeree Holder shall
again be subject to the co-sale rights of the Preferred Holders and shall
require compliance by the Offeree Holder with the procedures described in this
Section 5.1.

             (g) For purposes of any calculation of the number of shares of
Common Stock outstanding under this Section 5.1, and with respect to any
numerator or denominator provided herein, the conversion of all securities
convertible into or exchangeable for Common Stock and the exercise of all
outstanding options (other than options granted pursuant to the Company's 1995
Stock Option Plan) and warrants shall be assumed.

         5.2 Prohibited Transfers.

             (a) In the event an Offeree Holder should sell any Restricted
Founders Shares in contravention of the co-sale rights of the Preferred Holders
under Section 5.1 of this Agreement (a "Prohibited Transfer"), each Preferred
Holder, in addition to such other remedies as may be available at law, in equity
or hereunder, shall have the put option provided below, and the Offeree Holder
shall be bound by the applicable provisions of such option.


                                      -19-
<PAGE>   22


             (b) In the event of a Prohibited Transfer, each Preferred Holder
shall have the right to sell to the Offeree Holder the type and number of shares
of Common Stock equal to the number of shares each Preferred Holder would have
been entitled to transfer to the transferee had the Prohibited Transfer under
Section 5.1 hereof been effected pursuant to and in compliance with the terms
hereof. such sale shall be made on the following terms and conditions.

                 (i) The price per share at which the shares are to be sold to
the Offeree Holder shall be equal to the price per share paid by the transferee
to the Offeree Holder in the prohibited Transfer. The Offeree Holder shall also
reimburse each Preferred Holder for any and all fees and expenses, including
legal fees and expenses incurred pursuant to the exercise or the attempted
exercise of the Preferred Holder rights under Section 5.1

                 (ii) Within 90 days after the later of the dates on which the
Preferred Holder (A) receives notice of the prohibited Transfer or (B) otherwise
became aware of the Prohibited Transfer, each Preferred Holder shall, if
exercising the option created hereby, deliver to the Offeree Holder the
certificate or certificates representing share to be sold, each certificate to
be properly endorsed for transfer.

                 (iii) The Offeree Holder shall, upon receipt of the certificate
or certificates for the share to be sold by a Preferred Holder, pursuant to this
Section 5.2(b), pay the aggregate purchase price therefor and the amount of
reimbursable fees and expenses, as specified in Section 5.2(b)(i), in cash or by
other means acceptable to the Preferred Holder.

                 (iv) Notwithstanding the foregoing, any attempt by an Offeree
Holder to transfer Restricted Founders Shares in violation of Section 5.1 hereof
shall be void and the Company will not effect such a transfer nor will it treat
any alleged transferee as the holder of such shares without written consent of a
majority in interest of the Preferred Holders.

6.       Restrictive Legends and Restrictions on Transfer.

         6.1 Restrictive Legends.

             (a) Each certificate representing shares of Common Stock and
Preferred Stock or any other securities issued in respect of such Common Stock
and Preferred Stock upon any stock split, stock dividend, recapitalization,
merger, consolidation, or similar event, shall (unless otherwise permitted by
the provisions of Section 6.2 be stamped or otherwise imprinted with legends in
substantially the following form (in addition to any legend required under
applicable state securities laws) now or hereafter owned by the Common Holders
or Preferred Holders shall be endorsed with the following legends:

         THE SALE, PLEDGE, HYPOTHECATION OR TRANSFER OF THE SECURITIES
         REPRESENTED BY THIS CERTIFICATE IS SUBJECT TO THE TERMS AND CONDITIONS
         OF A CERTAIN AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT BY AND
         BETWEEN THE CORPORATION AND THE STOCKHOLDERS OF THE CORPORATION.



                                      -20-
<PAGE>   23


         COPIES OF SUCH AGREEMENT MAY BE OBTAINED UPON REQUEST TO THE SECRETARY
         OF THE CORPORATION.

         THE SALE AND ISSUANCE OF THE SECURITIES REPRESENTED BY THIS CERTIFICATE
         HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED
         (THE "ACT"), OR UNDER THE SECURITIES LAW OF ANY STATE OR OTHER
         JURISDICTION. THESE SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT AND
         NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE DISTRIBUTION THEREOF.
         THESE SECURITIES MAY NOT BE OFFERED, SOLD, PLEDGED, OR TRANSFERRED
         UNLESS A REGISTRATION STATEMENT UNDER THE ACT IS IN EFFECT AS TO THESE
         SECURITIES AND SUCH OFFER, SALE, PLEDGE, OR TRANSFER IS IN COMPLIANCE
         WITH APPLICABLE SECURITIES LAWS OF ANY STATE OR OTHER JURISDICTION OR
         THERE IS AN OPINION OF COUNSEL OR OTHER EVIDENCE, SATISFACTORY TO THE
         CORPORATION THAT AN EXEMPTION THEREFROM IS AVAILABLE AND THAT SUCH
         OFFER, SALE, PLEDGE, OR TRANSFER IS IN COMPLIANCE WITH APPLICABLE
         SECURITIES LAWS OF ANY STATE OR OTHER JURISDICTION.

             (b) Each Common Holder and Preferred Holder agrees that the Company
may instruct its transfer agent to impose transfer restrictions on the shares
represented by certificates bearing the legends referred to in Section 6.1(a)
above to enforce the provisions of this Agreement and the Company to promptly do
so. The first legend set forth in Section 6.1(a) shall be removed upon
termination of this Agreement pursuant to Section 7.6(a).

         6.2 Permitted Transfers. The Company shall be obligated to reissue
promptly certificates without the second legend set forth in Section 6.1(a) at
the request of any Holder thereof if the holder shall have obtained an opinion
of counsel (which counsel may be counsel to the Company) reasonably acceptable
to the Company to the effect that the securities proposed to be disposed of may
lawfully be so disposed of without registration, qualification or legend. Any
legend endorsed on an instrument pursuant to applicable state securities laws
and the stop-transfer instructions with respect to such securities shall be
removed upon receipt by the Company of an order of the appropriate blue sky
authority authorizing such removal.

         6.3 Notice of Proposed Transfers.

             (a) Prior to any proposed transfer of any Restricted Securities,
unless there is in effect a registration statement under the Securities Act
covering the proposed transfer, the Holder or Common Holder thereof shall give
written notice (the "Notice") to the Company of such Holder's or Common Holder's
intention to make such transfer. If reasonably requested by the Company prior to
the transfer being effected, the Holder or Common Holder shall provide to the
Company a written opinion of legal counsel who shall be reasonably satisfactory
to the Company, addressed to the Company and reasonably satisfactory in form and
substance to the Company's counsel, to the effect that the proposed transfer of
the Restricted Securities may be effected without registration under the


                                      -21-
<PAGE>   24


Securities Act. It is agreed that the Company will not require opinions of
counsel for transactions made pursuant to Rule 144 under the Securities Act
except in unusual circumstances. Notwithstanding the foregoing provisions of
this paragraph, no such registration statement or opinion of counsel shall be
necessary for a transfer by a holder which is (i) a partnership to its partners
or retired partners in accordance with partnership interests, or (ii) an
individual to a family member or trust for the benefit of such Holder, Common
Holder or a family member, provided the transferee will be subject to the terms
of this Section 6.3 to the same extent as if he were an original Holder or
Common Holder hereunder. Each certificate evidencing the Restricted Securities
so transferred shall bear the appropriate restrictive legends set forth in
Section 6.1, except that such certificate shall not bear the second restrictive
legend set forth in Section 6.1(a) if in the opinion of counsel for the Company
such legend is not required in order to establish compliance with any provisions
of the securities laws.

             (b) Each Holder and Common Holder consents to the Company making a
notation on its records and giving instructions to any transfer agent of the
Restricted Securities in order to implement the restrictions on transfer
described in this Section.

7.       Information Rights.

         7.1 Financial Information. The Company will furnish the following to
each Holder (or its representative) which, alone or together with entities
affiliated with such Holder, in the aggregate, owns at least 500,000 Restricted
Preferred Shares and to each Holder which represents that it is a "venture
capital operating company" for purposes of Department of Labor Regulation
Section 2510.3-101 and who requests them (in each case, a "Significant Holder"):

                 (i) as soon as practicable within 30 days after the end of each
month, an unaudited monthly statement of operations, statement of cash flows and
balance sheet, in each case prepared on a consolidated basis for the Company.
The monthly financial statements shall include comparisons to budget;

                 (ii) as soon as practicable after the end of each fiscal
quarter, and in any event within 45 days thereafter, statements of operations
and statements of cash flows for such fiscal quarter, balance sheets of the
Company as of the end of such fiscal quarter, in each case prepared on a
consolidated basis for the Company; and

                 (iii) as soon as practicable after the end of each fiscal year,
and in any event within 90 days thereafter, statements of operations and
statements of cash flows for such fiscal year, balance sheets of the Company as
of the end of such fiscal year, all certified by independent public accountants
of recognized national standing selected by the Company.

         All financial statements provided for above shall be prepared in
accordance with general accepted accounting principles applied on a consistent
basis (except that such unaudited financial statements may be prepared without
footnotes and will be subject to normal year-end audit adjustments).


                                      -22-
<PAGE>   25


         Each Significant Holder agrees that any information obtained by such
Significant Holder pursuant to this Section 7.1 which may be proprietary to the
Company or otherwise confidential shall not be disclosed without the prior
written consent of the Company; provided, however, that Chancellor LGT Asset
Management, Inc. may cause any information to be disclosed to Citiventure III
and to KME Venture III, L.P., each of which shall be bound by the
confidentiality provisions hereof. Each Significant Holder further acknowledges
and understands that any information so obtained which may be considered
"inside" non-public information will not be utilized by such Significant Holder
in connection with purchases and/or sales of the Company's securities except in
compliance with applicable state and federal antifraud statutes.

         7.2 Additional Information and Rights.

             (a) The Company will permit any Significant Holder to visit and
inspect any of the properties of the Company, including its books of account and
other records (and make copies thereof and take extracts therefrom), and to
discuss its affairs, finances and accounts with the Company's officers and its
independent public accountants, all at such reasonable times and as often as
such person may reasonably request.

             (b) The Company will deliver the reports described below in this
Section 7.2(b) to each Significant Holder:

                 (i) Annually (but in any event at least thirty (30) days prior
to the commencement of each fiscal year of the Company) the annual budget of the
Company, in such manner and form as approved by the Board of Directors of the
Company, which annual budget shall include a projection of income and a
projected cash flow statement for such fiscal year and a projected balance sheet
as of the end of such fiscal year. Any material changes in such annual budget
shall be submitted as promptly as practicable after such changes have been
approved by the Board of Directors of the Company.

                 (ii) With reasonable promptness, such other information and
data with respect to the Company and its subsidiaries as any such person may
from time to time reasonably request.

             (c) Each Holder who represents to the Company that it is a "venture
capital operating company" for purposes of Department of Labor Regulation
Section 2510.3-101 shall have the right to consult with and advise the officers
of the Company as to the management of the Company.

             (d) The provisions of Section 7.1 and this Section 7.2 shall not be
in limitation of any rights which any stockholder may have with respect to the
books and records of the Company and its subsidiaries, or to inspect their
properties or discuss their affairs, finances and accounts, under the laws of
the jurisdictions in which the Company is incorporated.

             (e) Anything in this Section 7 to the contrary notwithstanding, no
Significant Holder by reason of this Agreement shall have access to any trade
secrets or classified information


                                      -23-
<PAGE>   26


of the Company. Each Significant Holder hereby agrees to hold in confidence and
trust and not to misuse or disclose any confidential information provided
pursuant to this Section 7.2 (it being understood that Chancellor LGT Asset
Management, Inc., may cause any information provided to it to be disclosed to
Citiventure III and to KME Venture III, L.P., each of which shall be bound by
the confidentiality provisions hereof. Each Significant Holder shall notify the
Company in writing (which notice shall be delivered no less frequently than
annually) of such Significant Holder's ownership of any securities of entities
which such Significant Holder reasonably determines to be a competitor of the
Company.

8.       Voting and Other Covenants.

         8.1 Agreement to Vote. Each of the holders of Preferred Stock (and
their permitted assigns) and each of the Stockholders holding Common Stock (and
their permitted assigns) hereby agrees to vote all shares of the Company's
Preferred Stock or Common Stock now or hereafter owned by it, whether
beneficially or otherwise, at any regular or special meeting of stockholders of
the Company, or, in lieu of any such meeting, to give their written consent, as
provided in this Section 8.

         8.2 Voting Events. If there shall be submitted to the stockholders of
the Company any proposal concerning the election or removal of directors of the
Company, then each of the holders of Preferred Stock (and their permitted
assigns) and each of the Stockholders holding Common Stock (and their permitted
assigns) shall vote or act with respect to all shares of Preferred Stock or
Common Stock so as to elect to the board of directors of the Company, as the two
directors to be elected by the holders of Series A Preferred Stock and Series B
Preferred Stock, as the three directors to be elected by the holders of Series C
Preferred Stock and as two of the three directors to be elected by the holders
of Preferred Stock and Common Stock in accordance with Section 3(b) of Article V
of the Company's Amended and Restated Certificate of Incorporation, the
designees specified in Section 8.3 hereof.

         8.3 Designation and Election of Directors.

             (a) So long as any shares of Series A Preferred Stock or Series B
Preferred Stock shall be outstanding, the holders of Series A Preferred Stock
and the holders of Series B Preferred Stock, voting together, shall together
have the right to designate two directors for election to the Company's board of
directors in accordance with the provisions of this Section 8. The designation
made in accordance with the preceding sentence shall be made by the holders of a
majority of the issued and outstanding shares of Series A Preferred Stock and
Series B Preferred Stock.

             (b) So long as any shares of Series C Preferred Stock shall be
outstanding, the holders of Series C Preferred Stock shall have the right to
designate three directors (the "Series C Directors") for election to the
Company's board of directors in accordance with the provisions of this Section
8. So long as Schroder Ventures International Life Sciences Fund L.P. 1,
together with its affiliates (collectively, "Schroder"), holds at least
2,013,966 shares of Series C Preferred Stock, (as adjusted to reflect stock
dividends, splits, combinations and other recapitalizations), the designation of
one of the Series C Directors shall be made by Schroder. In the event Schroder
holds less than


                                      -24-
<PAGE>   27


2,013,966 shares of Series C Preferred Stock, (as adjusted to reflect stock
dividends, splits, combinations and other recapitalizations), the designation
made in accordance with the preceding sentence shall be made by the holders of a
majority of the issued and outstanding shares of Series C Preferred Stock. So
long as International BM Biomedicine Holdings, Inc., together with its
affiliates (collectively, "Biomedicine"), holds at least 2,209,945 shares of
Series C Preferred Stock, (as adjusted to reflect stock dividends, splits,
combinations and other recapitalizations), the designation of one of the Series
C Directors shall be made by Biomedicine. In the event Biomedicine holds less
than 2,209,945 shares of Series C Preferred Stock, , (as adjusted to reflect
stock dividends, splits, combinations and other recapitalizations), the
designation made in accordance with the preceding sentence shall be made by the
holders of a majority of the issued and outstanding shares of Series C Preferred
Stock. So long as Sprout Capital VII, L.P., together with its affiliates
(collectively, "Sprout"), holds at least 3,020,952 shares of Series C Preferred
Stock, , (as adjusted to reflect stock dividends, splits, combinations and other
recapitalizations), the designation of one of the Series C Directors shall be
made by Sprout. In the event Sprout holds less than 3,020,952 shares of Series C
Preferred Stock, , (as adjusted to reflect stock dividends, splits, combinations
and other recapitalizations), the designation made in accordance with the
preceding sentence shall be made by the holders of a majority of the issued and
outstanding shares of Series C Preferred Stock.

             (c) During the term of this Agreement, each of the Stockholders
agrees to vote the shares of Common Stock and Preferred Stock now or hereafter
owned by such Stockholder, whether beneficially or otherwise, so that one of the
directors elected pursuant to the provisions of Article V, Section 3(b) of the
Company's Amended and Restated Certificate of Incorporation by the holders of
Common Stock of the Company and the holders of the Preferred Stock of the
Company, voting together as a class, shall be the Company's Chief Executive
Officer.

             (d) During the term of this Agreement, each of the Stockholders
agrees to vote the shares of Common Stock and Preferred Stock now or hereafter
owned by such Stockholder, whether beneficially or otherwise, so that two of the
directors elected pursuant to the provisions of Article V, Section 3(b) of the
Company's Amended and Restated Certificate of Incorporation by the holders of
Common Stock of the Company and the holders of the Preferred Stock of the
Company, voting together as a class, shall be persons who are not affiliates of
the Company or of any of the Company's stockholders and who have experience in
the biotechnology industry.

         8.4 Successors in Interest. The provisions of this Section 8 shall be
binding upon the successors in interest of any of the shares of the Preferred
Stock or any of the shares of Common Stock held by Stockholders. The Company
shall not permit the transfer of any shares of Preferred Stock or any shares of
Common Stock held by a Stockholder on its books or issue a new certificate
representing any shares of Preferred Stock or Common Stock held by a Stockholder
unless and until the person to whom such security is transferred shall have
executed a written agreement pursuant to which such person becomes subject to
the provisions of this Section 8 and agrees to be bound by all the provisions
hereof.

         8.5 Conversion Stock. The provisions of Section 8.3(a) and Section
8.3(b) shall not apply to any shares of Common Stock issued or issuable upon
conversion of the Preferred Stock.


                                      -25-
<PAGE>   28


9.       Miscellaneous.

         9.1 Conditions to Exercise of Rights. Exercise of the Holders' rights
under this Agreement shall be subject to and conditioned upon, and each Holder
and the Company shall use its or his best efforts to assist each Holder in,
compliance with applicable laws.

         9.2 Repurchase Agreement. This Agreement is subject to, and shall in no
manner limit the right of the Company to repurchase securities from a Founder at
cost pursuant to any stock restriction agreement or other agreement between the
Company and the Founder.

         9.3 Governing Law. This Agreement shall be governed by and construed in
accordance with the laws of the State of Delaware.

         9.4 Amendment. Any provision may be amended and the observance thereof
may waived (either generally or in a particular instance), only by the written
consent of the Company and Holders holding more than fifty percent (50%) in
interest of the Registrable Securities which are issued or issuable in respect
of Series A Preferred Stock of the Company and Holders holding more than fifty
percent (50%) in interest of the Registrable Securities which are issued or
issuable in respect of Series B Preferred Stock of the Company and Holders
holding more than fifty percent (50%) in interest of the Registrable Securities
which are issued or issuable in respect of Series C Preferred Stock of the
Company; provided, however, that any amendment or waiver of any provisions of
Sections 2 or 5 or 8.3(c) or 8.3(d) also requires the written consent of the
Common Holders holding more than fifty percent (50%) in interest of the
Restricted Founders Shares. Any amendment or waiver effected in accordance with
this paragraph shall be binding upon each Holder, Common Holder, its successors
and assigns, heirs, executors and the Company.

         9.5 Assignment of Rights. This Agreement and the rights and obligations
of the parties hereunder shall inure to benefit of and be binding upon, their
respective successors, assigns and legal representatives. The provisions of
Section 4.6 shall also inure to the benefit of each Indemnified Party.

         9.6 Term.

             (a) Sections 2, 3, 5, 7 and 8 of this Agreement shall terminate
upon the earlier of (i) the closing of a firm commitment underwritten public
offering pursuant to an effective registration statement under the Securities
Act of 1933, as amended, covering the offer and sale of Common Stock for the
account of the Company and/or selling stockholders to the public at such per
share price and resulting in such aggregate net proceeds to the Company and/or
the selling stockholders (after deducting underwriters' discounts and expenses
relating to the issuance) as would result in the automatic conversion of the
Company's Preferred Stock pursuant to the Company's Amended and Restated
Certificate of Incorporation, and (ii) the closing of the sale of all or
substantially all of the Company's assets or the acquisition of the Company by
another entity by means of merger or consolidation resulting in the exchange of
the outstanding shares of the Company's capital stock for securities or
consideration issued, or caused to be issued, by the acquiring entity or by the
acquiring company's parent or subsidiary.


                                      -26-
<PAGE>   29


             (b) No Holder shall be entitled to exercise any rights provided for
in Section 4 of this Agreement after five (5) years following a firm commitment
offering of the type described in Section 9.6(a)(i).

         9.7 Notices. Unless otherwise stated herein, all notices required or
permitted hereunder shall be in writing and shall be deemed effectively given
upon personal delivery to the party to be notified or five days after deposit in
the United States mail, by registered or certified mail, postage prepaid, or
otherwise delivered by hand, facsimile or messenger and properly addressed to
the party to be notified as set forth on the signature page hereof or at such
other address as such party may designate by ten (10) days' advance written
notice to the other parties hereto.

         9.8 Severability. In the event one or more of the provisions of this
Agreement should, for any reason, be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not affect any other provisions of this Agreement, and this Agreement
shall be construed as if such invalid, illegal or unenforceable provision had
never been contained herein.

         9.9 Attorney Fees. In the event that any dispute among the parties to
this Agreement should result in litigation, the prevailing party in such dispute
shall be entitled to recover from the losing party all fees, costs and expenses
of enforcing any right of such prevailing party under or with respect to this
Agreement, including without limitation, such reasonable fees and expenses of
attorneys and accountants, which shall include, without limitation, all fees,
costs and expenses of appeals.

         9.10 Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be deemed an original and enforceable against
the parties actually executing such counterpart, and all of which together shall
constitute one instrument.

         9.11 Entire Agreement. This Agreement constitutes the entire agreement
between the parties relative to the specific subject matter hereof. Any previous
agreement among the parties relative to the specific subject matter hereof is
superseded by this Agreement.

         9.12 Aggregation of Stock. All Shares held or acquired by affiliated
entities or persons shall be aggregated together for the purpose of determining
the availability of any rights under this Agreement. For purposes of
aggregation, Citiventure III and KME Venture III, L.P. shall be considered
affiliates of each other.



                                      -27-
<PAGE>   30


         The foregoing Fourth Amended and Restated Stockholder Rights Agreement
is hereby executed as of the date first above written.


                                     ALLOS THERAPEUTICS, INC.

                                     By: /s/ Stephen Hoffman
                                        ----------------------------------------

                                     Title: President
                                           -------------------------------------

                                     Address:     7000 North Broadway
                                                  Suite 400
                                                  Denver, CO  80221


<PAGE>   31



ABINGWORTH BIOVENTURES SICAV

By: /s/ M.-Rose Doch  /s/ Fernand Heim
   -----------------------------------
    Director          Mandatory
    Abingworth Bioventures SICAV

Address:  231 Valdes Bons Malades
          Kirchberg 2121
          Luxembourg



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   32


/s/ Donald J. Abraham
--------------------------------------
Donald J. Abraham


NANCY W. ABRAHAM, TRUSTEE,
  U/A 12-14-94

By: /s/ Nancy W. Abraham
   -----------------------------------

Title: Trustee
      --------------------------------

Address:  3511 Buckhead Rd.
          Midlothian, VA 23113


ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   33


/s/ Stephen J. Hoffman
--------------------------------------
Stephen J. Hoffman

Address:  7000 North Broadway
          Suite 400
          Denver, CO  80221



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   34



A. P. INVESTMENT CORPORATION

/s/ James B. Farinholt, Jr.
--------------------------------------
James B. Farinholt, Jr.

Title: President
      --------------------------------

Address:  Westham Green #77
          300 North Ridge Road
          Richmond, VA 23229



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   35



VIRGINIA COMMONWEALTH UNIVERSITY
INTELLECTUAL PROPERTY FOUNDATION

By: /s/ Richard C. Franson
   -----------------------------------

Title: President VCU-IPF, Director,
       Office of Technology Transfer
      --------------------------------

Address:  Director of Technology Transfer
          Virginia Commonwealth University
          P.O. Box 980568
          Richmond, VA  23298-0568



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   36



DRAKE & CO FOR THE ACCOUNT OF CITIVENTURE III

By: /s/ Michael Going
   -----------------------------------
   its



KME VENTURE III, L.P.

BY: INVESCO Private Capital Inc.
    as investment manager and
    attorney-in-fact

By: /s/ Paing Saxeva
   -----------------------------------
   Paing Saxeva, Managing Director

Address:  INVESCO Private Capital, Inc.
          1166 Avenue of the Americas
          New York, NY 10036
          Attn: Mark Radovanovich



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   37



JOHNSON & JOHNSON DEVELOPMENT
  CORPORATION

By: /s/ Ting Pau Oei
   -----------------------------------

Title: Vice President
      --------------------------------

Address:  1 Johnson & Johnson Plaza
          New Brunswick, NJ  08933





ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   38



BAYVIEW INVESTORS, LTD.

By: /s/ [ILLEGIBLE]
   -----------------------------------

Title: Authorized Signatory
      --------------------------------

Address:  555 California Street, 23rd Floor
          San Francisco, CA  94104




ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   39



MARQUETTE VENTURE PARTNERS II, L.P.

By: MARQUETTE GENERAL II, its General Partner

By: /s/ James E. Daverman
   -----------------------------------
   James E. Daverman or Lloyd D. Ruth
   Authorized Signatory



MVP II AFFILIATES FUND, L.P.

By:   MARQUETTE GENERAL II, its General Partner

By: /s/ James E. Daverman
   -----------------------------------
   James E. Daverman or Lloyd D. Ruth
   Authorized Signatory

Address:  520 Lake Cook Road
          Suite 450
          Deerfield, IL  60015




ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   40



SCHRODER VENTURES INTERNATIONAL LIFE SCIENCES FUND L.P. 1

By: SCHRODER VENTURE MANAGERS INC., its General Partner

By: /s/ Nicola Lawson  /s/ Deborah Speight
   ---------------------------------------
Name: Nicola Lawson        Deborah Speight
     -------------------------------------
Title: Directors and V.P.s
      ------------------------------------


SCHRODER VENTURES INTERNATIONAL LIFE SCIENCES FUND L.P. 2

By: SCHRODER VENTURE MANAGERS INC., its General Partner

By: /s/ Nicola Lawson  /s/ Deborah Speight
   ---------------------------------------
Name: Nicola Lawson        Deborah Speight
     -------------------------------------
Title: Directors and V.P.s
      ------------------------------------

Address:  Schroders Inc.
          787 Seventh Avenue, 34th Floor
          New York, New York  10019



SCHRODER VENTURES INTERNATIONAL LIFE SCIENCES TRUST

By:   CODAN TRUST COMPANY LIMITED, as Trustee

By:   SCHRODER VENTURE MANAGERS LIMITED, as Attorney-in-Fact

By: /s/ Nicola Lawson  /s/ Deborah Speight
   ---------------------------------------
Name: Nicola Lawson        Deborah Speight
     -------------------------------------
Title: Directors
      --------------------------------



SCHRODER VENTURE MANAGERS LIMITED, as Manager of the Co-Investment Scheme

By: /s/ Nicola Lawson  /s/ Deborah Speight
   ---------------------------------------
Name: Nicola Lawson        Deborah Speight
     -------------------------------------
Title: Directors
      --------------------------------

Address:  Schroders (Bermuda) Limited
          22 Church Street
          Hamilton HM 11
          Bermuda



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   41



DLJ CAPITAL CORP.

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon
Its: Attorney In Fact



DLJ ESC II, L.P.

By:   DLJ LBO Plans Management Corporation

Its:  Manager

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon
Its:  Attorney In Fact



SPROUT CAPITAL VII, L.P.

By:   DLJ CAPITAL CORP
Its:  Managing General Partner

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon
Its:  Attorney In Fact



THE SPROUT CEO FUND, L.P.

By:   DLJ CAPITAL CORP
Its:  General Partner

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon
Its:  Attorney In Fact

Address:  3000 Sand Hill Road
          Building 3, Suite 170
          Menlo Park, CA  94025



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   42


SPROUT CAPITAL VIII, L.P.

By: DLJ CAPITAL CORPORATION

Its: Managing General Partner

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon

Its: Attorney In Fact



SPROUT VENTURE CAPITAL, L.P.

By: DLJ Capital Corporation

Its: General Partner

By: /s/ Philippe Chambon
   -----------------------------------
   Philippe Chambon

Its: Attorney In Fact

Address:  3000 Sand Hill Road
          Building 3, Suite 170
          Menlo Park, CA 94025



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   43



--------------------------------------
Paul Baryames


--------------------------------------
Louis Berneman

/s/ Jon S. Saxe
--------------------------------------

/s/ Myrna G. Marshall
--------------------------------------
Jon S. Saxe and Myrna G. Marshall
as joint tenants with right of survivorship

/s/ Jeffrey S. Vender
--------------------------------------
Jeffrey S. Vender

/s/ John T. Greff
--------------------------------------
John T. Greff

/s/ Michael J. Gerber
--------------------------------------
Michael J. Gerber


--------------------------------------
Matthew Gibbs

/s/ Elizabeth Crump
--------------------------------------
Elizabeth Crump


--------------------------------------
Susan Quagliata



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   44



OAK V AFFILIATES FUND,
  LIMITED PARTNERSHIP

By:   OAK V AFFILIATES,
      its General Partner

By: /s/ Ann H. Lamont
   -----------------------------------
   Ann H. Lamont, General Partner

Address:  One Gorham Island
          Westport, CT 06880



OAK INVESTMENT PARTNERS V,
  LIMITED PARTNERSHIP

By:   OAK ASSOCIATED V, LLC
        its General Partner

By: /s/ Ann H. Lamont
   -----------------------------------
   Ann H. Lamont, Managing Member

Address:  One Gorham Island
          Westport, CT 06880




ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   45



BIOTECHNOLOGY DEVELOPMENT FUND, L.P.

By:   BioAsia Investments, LLC
Its:  General Partner

      By: /s/ Frank Kung
         -----------------------------
              Frank Kung
      Its:    Managing Member







ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   46



SEQUEL LIMITED PARTNERSHIP

By:   Sequel Venture Partners L.L.C.
Its:  General Partner

      By: /s/ Kinney Johnson
         -----------------------------

      Name:
           ---------------------------
      Its:    Manager



SEQUEL EURO LIMITED PARTNERSHIP

By:   Sequel Venture Partners L.L.C.
Its:  General Partner

      By: /s/ Kinney Johnson
         -----------------------------

      Name:
           ---------------------------
      Its:    Manager

Address:  4430 Arapahoe Avenue
          Suite 220
          Boulder, CO  80303

ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   47



INTERNATIONAL BM BIOMEDICINE HOLDINGS, INC.

      By: /s/ G. Blum
         -----------------------------

      Name: Dr. G. Blum
           ---------------------------
      Its: Chairman of the Board




      By: /s/ F. Keiser
         -----------------------------

      Name: F. Keiser
           ---------------------------
      Its: CEO




ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   48


CALVERT SOCIAL INVESTMENT FUND BALANCED PORTFOLIO

By: /s/ Susan Walker Bender
   -----------------------------------
   Susan Walker Bender
Title: Assistant Secretary

Address:  Calvert Social Investment Fund Balanced Portfolio
          4550 Montgomery Ave., Suite 1000N
          Bethesda, MD  20814
          ATTN:  Susan Walker Bender




ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   49


BARBARA PIETTE


/s/ Barbara Piette
--------------------------------------

Address:  93 Mt. Vernon Street
          Boston, MA  02108



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   50


                                   EXHIBIT A

          STOCKHOLDERS TO THE FOURTH AMENDED AND RESTATED STOCKHOLDER
                                RIGHTS AGREEMENT
<PAGE>   51



EXHIBIT A

Abingworth Bioventures SICAV

Donald J. Abraham

Nancy W. Abraham, Trustee U/A 12-14-94

A. P. Investment Corporation

Center for Innovative Technology, Inc.

Drake & Co for the Account of Citiventure III

KME Venture III, L.P.

Stephen J. Hoffman

Johnson & Johnson Development Corporation

Marquette Venture Partners II, L.P.
MVP II Affiliates Fund, L.P.

Oak V Affiliates Fund, Limited Partnership
Oak Investment Partners V, Limited Partnership

ADDED JUNE 26, 1996, PURSUANT TO AMENDMENT AGREEMENT DATED JUNE 26, 1996:
Paul Baryames
Louis Berneman
Jon S. Saxe and Myrna G. Marshall as joint tenants with right of survivorship
Jeffrey S. Vender
John T. Greff
Michael J. Gerber
Matthew Gibbs
Elizabeth Crump
Susan Quagliata



ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT
<PAGE>   52



ADDED AUGUST 1, 1996, PURSUANT TO CIT TRANSFER:
Mona Mahran
Ahmed Mehanna
Ramnarayan Randad
Virginia Commonwealth University Intellectual Property Foundation

ADDED SEPTEMBER 4, 1996, PURSUANT TO DONALD ABRAHAM TRANSFER:
Gajanan S. Joshi

ADDED JANUARY 13, 1998, PURSUANT TO SERIES C CONVERTIBLE PREFERRED STOCK
PURCHASE AGREEMENT:
Schroder Ventures International Life Sciences Fund L.P. 1
Schroder Ventures International Life Sciences Fund L.P. 2
Schroder Ventures International Life Sciences Trust
Schroder Venture Managers Limited
DLJ Capital Corp.
DLJ ESC II, L.P.
Sprout Capital VII, L.P.
The Sprout CEO Fund, L.P.
Bayview Investors, Ltd.
Joshua Lederberg

ADDED MAY 4, 1998, PURSUANT TO AMENDMENT AGREEMENT DATED MAY 4, 1998:
Biotechnology Development Fund, L.P.
Biotechnology Development Fund III, L.P.
Sequel Limited Partnership
Sequel Euro Limited Partnership

ADDED MAY 11, 1998, PURSUANT TO TRANSFER FROM STEPHEN J. HOFFMAN
Barbara Dau Southwell

ADDED OCTOBER 4, 1999, PURSUANT TO SERIES C CONVERTIBLE PREFERRED STOCK
PURCHASE AGREEMENT:
International BM Biomedicine Holdings, Inc.
Calvert Social Investment Fund Balanced Portfolio
Barbara Piette
Sprout Capital VIII, L.P.
Sprout Venture Capital, L.P.


ALLOS THERAPEUTICS, INC.
FOURTH AMENDED AND RESTATED STOCKHOLDER RIGHTS AGREEMENT