Exhibit 99.1

CONFIDENTIAL PORTIONS OF THIS EXHIBIT HAVE BEEN OMITTED PURSUANT TO REGULATION
240.24B-2B OF THE SECURITIES EXCHANGE ACT OF 1934.  [*] INDICATES OMITTED
MATERIAL THAT IS THE SUBJECT OF A CONFIDENTIAL TREATMENT REQUEST AND IS FILED
SEPARATELY WITH THE COMMISSSION.




                            Participation Agreement

                         - Atugen Biotechnology GmbH -


                                      -2-



                            Participation Agreement

                                     Among

1.    RIBOZYME PHARMACEUTICALS, Inc.,
      2950 Wilderness Place
      Boulder, Colorado
      USA

                                     -  hereinafter referred to as "Founder 1" -

2.    Dr. Ralph Earl Christoffersen
      1995 Stony Hill
      Boulder, Colorado 80303
      USA

                                     -  hereinafter referred to as "Founder 2" -

3.    Mr. Lawrence E. Bullock
      8550 Waterford Way.
      Longmont, CO 80503
      USA
                                     -  hereinafter referred to as "Founder 3" -

4.    Dr. Nassim Usman
      2129 Night Sky Lane,
      Lafayette, CO 80026
      USA
                                     -  hereinafter referred to as "Founder 4" -

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5.    Dr. James Thompson
      2925 Glenwood Drive # 103
      Boulder, CO 80301
      USA

                                     -  hereinafter referred to as "Founder 5" -

6.    Ms. Alene Holzman
      971 6th Street,
      Boulder, CO 80302
      USA

                                     -  hereinafter referred to as "Founder 6" -

7.    Dr. Thomas H. Rossing
      13781 N. 115th St.
      Longmont, CO 80501

                                     -  hereinafter referred to as "Founder 7" -

8.    Dr. Jorg Potzsch
      Pradelstrasse 9
      13187 Berlin

                                      - hereinafter referred to as "Founder 8" -

9.    Dr. Thomas Walther
      Dunckerstrasse 34
      10439 Berlin

                                      - hereinafter referred to as "Founder 9" -

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                                      -4-

- - the parties 1 to 9 hereinafter jointly referred to as "Founders" -

10.   Atugen Biotechnology GmbH,
      Maxmimilianstr. 35,
      80539 Munchen
      Germany

                               - hereinafter referred to as the "Company" -

11.   BB BioVentures L. P.
      One Cambridge Center, 9th Floor
      Cambridge, Massachusetts 02142
      USA
                               - hereinafter referred to as the "Investor" -


                                    Preamble

The Founders hold all the shares of the Company Atugen Biotechnology GmbH  with
its seat in Munich (application pending for transfer of seat to Berlin)
registered in the  Trade Register of the local court of Munich under HRB 119609.

The Founders  intend to increase the share capital of the Company in order to
provide the Company with new operating funds. Within the framework of this
capital increase, the Investor shall be given the opportunity to purchase up to
a maximum of 36.65% of the shares in total after the capital increase has
been effected at a closing (the "Closing") as set out in column titled
"Percentage of Share Holding After the First Closing" of annex 20 on a fully
diluted basis.


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The Investor is, inter alia, a capital investment fund which exists partly
for the purpose of making private investments in young companies with
technologically progressive products and for providing the means for business
expansion.

The basis of the Investor's decision to invest is, among other things, the Term
Sheet of June 16, 1998 agreed  to and signed by the Founders (annex 1) and the
business plan as amended on  July 30, 1998 (annex 2).

In view of these interests the parties conclude the following Participation
Agreement:

                                     Part 1
                                     ------
                                 Participation
                                 -------------
                                     (S) 1
                              Increase of Capital

1.    Today the Founders will increase the share capital of the Company by
      DM 30,600 from DM 50,000 to DM 80,600 with a shareholders' resolution,
      recorded by a notary, whereby solely the Investor is allowed to subscribe
      the new Shares.

      The Investor is allowed to subscribe to a share in the amount of

                                   DM 30,600

      created by the increase of  capital. The investor shall assume the new
      original capital contribution and  pay, in addition to the nominal value
      of the new share, a surcharge to be allocated to the Company's reserves
      (EK04) in the total amount of DM 12,696,246.

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                                      -6-



2.    The Founders agree to waive their subscription right. Only the Investor is
      allowed to take over the new share.

3.    The Investor commits itself to subscribe to the new share through a
      separately notarized declaration and to pay, in addition to the nominal
      value of the new share, a surcharge to be allocated to the Company's
      reserves (EK04) in the total amount of DM 12,696,246.

4.    The new original capital contribution of DM 30,600 shall be paid in full
      before the registration of the capital increase, and the surcharge in the
      total amount of DM 12,696,246 shall be paid immediately after the
      registration of the capital increase in the Trade Register to the
      Company's bank account at the [*] with the account number [*] provided (i)
      the parties to this Agreement have by then executed a Vote Pooling
      Agreement concerning the election of the Advisory Council members and the
      transfer of the Company from GmbH to AG, satisfactory to the Investor; and
      (ii) the Company shall have received by then the grant funding contract or
      binding commitment letter from BMBF and the Senate of Berlin in the same
      amount as outlined in the letters of intent of those institutions
      contained in annex 18 and annex 19 as well as reports of a positive
      decision by tbg and regarding the GA-Grant funding; and (iii) the Founder
      1 has completed, on or before September 30, 1998, certain amendments, as
      previously discussed with the Investor, to its existing "Stock Purchase
      Agreement" and the "Research, License, Supply and Royalty Agreement" with
      Schering AG Company; (iv) all liens and encumbrances on the intellectual
      property to be transferred by Founder 1 to the Company pursuant to the
      License Agreement (Annex 14) shall be released and extinguished; and (v)
      all other agreements to be executed and delivered prior to the Closing
      shall have been so executed and delivered and any funding due thereunder
      shall have been received by the Company.

5.    Founder 1's participation in this Agreement is contingent upon Founder 1
      completing, on or before September 30, 1998, certain amendments, as
      previously discussed with the Investor, to its existing "Stock Purchase
      Agreement" and the "Research, License, Supply and Royalty Agreement" with
      Schering AG Company (which amendments shall be the same amendments
      referred to above).

6.    In the event that the conditions to the payment by the Investor of DM
      12,696,246 surcharge (as set forth in (S)1, paragraph 4 above) have not
      been fulfilled before January 1, 1999,


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                                      -7-


      the Investor will transfer its entire share of the Company to Founder 1
      for the nominal amount of DM 30,600; provided however, that the Investor
      will not be obligated to make such transfer if Founder 1 has materially
      breached this Agreement or failed to use its best efforts to satisfy those
      conditions to the payment of the surcharge which was within its control.

                                     (S) 2
            Transformation into an AG (German Stock Corporation) and
                             Employee Participation

1.    The parties will transform the Company into an Aktiengesellschaft (German
      stock corporation), changing its legal form before September 30, 1998,
      provided that the terms of the restructuring, as set forth in the
      documents to be prepared in connection therewith, are acceptable to the
      Investor. In the course of the Company's conversion into an AG, the -
      Investor's shares will be changed into preferred convertible stock with
      voting rights and liquidation preference ("Vorzugsaktien") as outlined in
      annex 17 and the founders' shares will be changed into common stock.
      Furthermore, Founder 1 will convert its shareholder loan in the amount of
      $10 Mio to be paid over the next 5 years into a shareholder contribution
      (EK04) still to be made available to the Company in the same time period.

2.    The Founders and the Investor will use their best efforts to agree to the
      terms of and to establish an employee stock option model based on the Term
      Sheet of June 16, 1998 (annex 1), probably in the form of a right to
      convert options into shares ("naked warrants"), to boost the motivation of
      the employees of the Company after its transformation into an AG.

3.    The documents to be agreed upon in the course of the conversion will
      conform as close as possible to the originally agreed corporate documents.


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                                      -8-

                                     Part 2
                                     ------
                                     (S) 3
                           Assurances and Warranties

In concluding this Agreement, the Investor assumes the veracity of the
statements and explanations given by the Founders and the Company in this
Agreement including annexes, especially the following ones. The Founders and the
Company are aware that the information contained in this Agreement, aside from
the examinations and investigations carried out by the Investor, is the basis of
the Investor's participation. The Founders, subject to the limitations of Part 3
(S) 4, section 1, declare explicitly and stand behind the following declarations
as complete and correct as of the date of this Agreement and as of the date of
Closing, insofar as the following individual explanations do not refer to
specific shareholders, as an independent guarantee in the sense of (S) 305 of
the Bugerliches Gesetzbuch (German Civil Code).

I.    Establishment and  Continued Existence
      1.    The Company was established on February 5, 1998 under the name "RM
            9810 Vermogensverwaltungs GmbH" and registered with the Local Court
            of Munich in the Trade Register under 119609. This is a legally
            effective Company with limited liability (GmbH) in accordance with
            the provisions of the GmbHG (Private Limited Company Act).

      2.    The Founder 1 acquired on May 5, 1998 all shares of capital of the
            Company, changed the Company's name to "Atugen Biotechnology GmbH",
            amended and restated the Articles of Association and applied to move
            the Company's seat to Berlin, on June 10, 1998, and finally split
            its share with the nominal amount of DM 50,000 into one partial
            share with the nominal amount of DM 46,000 and four small partial
            shares and sold the latter ones to the Founders 2, 8 and 9 as well
            as to the Founders 3 to 7 who are holding their share in the nominal
            amount of DM 1,600

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                                      -9-


            jointly. There are no other shares of capital stock of the Company
            issued or outstanding.

            The Company has never adopted or maintained any stock option plan or
            granted any stock options, and there are no options, warrants,
            calls, rights, commitments or agreements of any character, written
            or oral, to which the Company is a party or by which it is bound or
            committed to issue, deliver, sell, repurchase, or redeem, or cause
            to be issued, delivered, sold, repurchased or redeemed, any shares
            of the capital stock of the Company, or obligating the Company to
            issue any such option, with the exception of provisions under Annex
            11, warrant call, right, commitment or agreement.

            The Company has the right to conduct its business in its present
            form and has all requisite power and authority to enter into this
            Agreement and any other Related Agreements to which it is a party
            and to consummate the transactions contemplated hereby and thereby.
            The execution and delivery of this Agreement and the Related
            Agreements to which the Company is a party have been duly authorized
            by all corporate action on the part of the Company, and no further
            action on the part of the Company is required to authorize the
            Agreement, the Related Agreements and the transactions contemplated
            hereby and thereby. For purposes of this Agreement, the term
            "Related Agreements" shall mean ancillary agreements contemplated by
            this Agreement to be executed and delivered in connection with the
            transactions contemplated hereby.

      3.    The object of the enterprise is the research, development, and
            commercialization of biotechnological and pharmaceutical products
            and services, however not for the ultimate consumer. Excluded from
            the foregoing is, in particular, the production of such products
            whose purpose is the de-

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                                      -10-


            livery to others as far as pharmaceutical drugs are qualified in the
            sense of the Pharmaceutical Product Law.

      4.    The Founders have given the Investor a copy of the June 10, 1998
            version of the Articles of Association (annex 3) which is the
            current registered version. Supplementary contracts and additional
            agreements affecting shareholders' rights do not exist.

      5.    The excerpt from the Trade Register in Munich/Berlin as seen in
            annex 4 shows the current legal position correctly and completely
            with the exception of the appointment of Dr. Potzsch as general
            manager which has been effected by a shareholders' meeting of July
            10, 1998, but has not yet been registered in the trade register
            because of the pending seat transfer to Berlin.

      6.    The only persons entitled to represent the Company and to execute
            documents on its behalf according to its Articles of Association and
            otherwise solely are:

                         Dr. Ralph Earl Christoffersen

                                Dr. Jorg Potzsch

      7.    The nominal share or capital of the Company amounts to DM 50,000. It
            is fully paid, and  refund payments have not occurred since the
            acquisition of the shares through the Founders or earlier.

      8.    The present shareholders of the Company and the nominal shares
            distributed to them are stated in annex 5.

            The Founders 1, 2, 8 and 9 each hold their shares as sole owners in
            their own name and on their own account. The Founders 3 to 7 hold
            their share jointly in their name and on their own account. All of
            the shares,

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                                      -11-

            with the exception of provisions under Annex 11, are free of any
            rights of third parties, of whatever sort, and there are no claims
            for the grant of such rights or the transfer of shares. The shares
            are in particular not pledged or attached or burdened. With the
            exception of the obligations resulting from the Articles of
            Association with regard to shares of capital, there are in
            particular no right of pre-emption, options or similar rights of
            third parties. The shares are not subject to executorship or the
            conditions of provisional or reversionary succession.

      9.    Silent shareholders, partiaric loans, royalties or other obligations
            in regard to the distribution  of  the profits and losses of the
            Company do not exist.

      10.   Apart from the Articles of Association of the Company listed in
            Annex 3 and other Agreement, resolutions, and promises mentioned
            explicitly in this Agreement and its annexes, there are neither any
            contracts, resolutions nor promises of  any which would regulate the
            relationship between the Company and the shareholders or the legal
            relationships of the Company or the appointments to a body of the
            Company or obligations to conclude such contracts, resolutions or
            promises.

      11.   At no time has a petition to open bankruptcy/composition proceedings
            with regard to the assets of the Company or a winding-up resolution
            been made.

II.  Declarations with of Assets and Financial Standing

      1.a)   The Company has no binding obligations with regard to taxes or
            social insurance contributions or other contributions for an
            employee's pension, warranty or guarantee contracts, bills of
            exchange or suretyships.


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      1.b)  Pension obligations do not exist. Promises for pensions have not
            been made.

      1.c)  The Company has no contingent liability arising from suretyships,
            guarantees, etc. with the exception of the normal warranties arising
            within the framework of the proper Company management. The same
            applies to all shareholders of the Company in relation to the
            Company.

      1.d)  Hidden distributions of profits did not occur.

      1.e)  The Company is not overindebted or insolvent.

      2.    The Company is entitled to the full, exclusive and unencumbered
            ownership of each of the assets of the Company at the moment of the
            capital increase including, but not limited to full, unlimited and
            unencumbered ownership or exclusive licenses as set out in annex 14
            and also possession of all tangible and intangible assets which
            currently serve the business activity of the Company or which are
            designated to serve it. The assets of the Company are not liable for
            the obligations of third parties.

      3.    Since the date of its formation, the Company has been managed within
            the framework of the normal and proper course of business. Since its
            establishment, no material business incidents or legal transactions
            have occurred or were undertaken, and no event which individually or
            in conjunction with other events which did or could have
            substantially, negatively influenced the assets or profit margin of
            the Company occurred

      4.    Since the date of its formation, the Company has not suffered any
            damages or losses which individually or together could have a
            material effect on the Company or its financial status. No
            distribution of profits or decisions regarding the distribution of
            profits have occurred since the acquisition of the shares by the
            founders.

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                                      -13-

      5.    The Company owns no real estate.

III.  Other Declarations

      1.    Neither the Company nor the Founders and their direct relatives hold
            shares in other enterprises which operate in the field of the
            Company (as described in Annex 2) or a direct competitor of the
            Company or have business relations with the Company except for
            holdings detailed in annex 6.

      2.    The Founders each individually declare that they are not the owner
            of any intellectual property rights (patents, licenses, other
            intellectual property rights) on the basis of which any royalty
            payment could be demanded from the Company or the Company's business
            conduct could be impeded or  prohibited world-wide with the
            exception of the patents and patent applications of Founder 1 in
            accordance with annex 13 which are subject to licenses to the
            Company through the license agreement drafted in annex 14 and the
            Service Agreement drafted in annex 15.

            (a)  Annex 21 contains a complete and accurate list of all (i)
                 patented or registered intellectual property rights owned by
                 the Company or owned by Founder 1 and being transferred to the
                 Company in connection with the transactions contemplated
                 herein, (ii) pending patent applications and applications for
                 registrations of other intellectual property rights filed by
                 Founder 1 which relate to the technology to be transferred to
                 the Company, (iii) material unregistered trade names and
                 corporate names owned by the Company, (iv) material
                 unregistered trademarks, service marks, copyrights, mask works
                 and computer software owned by the Company and (v) all other
                 intellectual property rights owned by the Company

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                                      -14-


                 that are material to the operation of the business of the
                 Company as presently conducted and as presently proposed to be
                 conducted. The items listed on Annex 21 constitute all of the
                 intellectual property and intellectual property rights
                 necessary for the operation of the Company's business as
                 contemplated by this Agreement and the other agreements
                 contemplated hereby.

            (b)  Annex 22 also contains a complete and accurate list of (i) all
                 material licenses and other rights granted by the Company to
                 any third party with respect to any intellectual property
                 rights, except with respect to rights granted to customers of
                 the Company with respect to the Company's products in the
                 ordinary course of business, (ii) all material licenses and
                 other rights granted by Founder 1 to any third party with
                 respect to any intellectual property rights to be transferred
                 to the Company, and (iii) to the extent not disclosed pursuant
                 to Paragraph 1(a), all licenses and other rights material to
                 the operation of the businesses of the Company as presently
                 conducted and as presently proposed to be conducted, free and
                 clear of all liens or encumbrances granted by any third party
                 to the Company with respect to any intellectual property
                 rights, in each identifying the subject intellectual property
                 rights.

            (c)  Except to the extent set forth Annex 21 and the schedule of
                 exceptions, (i) the Company and Founder 1 collectively own all
                 right, title and interest in and to all of the intellectual
                 property rights listed or required to be listed on Annex 21
                 pursuant to Section 2(a), free and clear of all liens or
                 encumbrances; (ii) the Company will have pursuant to the
                 license granted by Founder 1, a valid license to all
                 intellectual property rights not owned by Founder 1 that are
                 material to the operation of the contemplated businesses of the
                 Company as presently conducted and as presently proposed to be
                 conducted (including but not

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                                      -15-

                 limited to those intellectual property rights listed on Annex
                 21 pursuant to Sections 2(a), and (b)), free and clear of all
                 liens or encumbrances, and such license or licenses will not be
                 terminated as a result of or require any third party consent to
                 effect an effective transfer via the license to the Company;
                 (iii) the conduct of the Founder 1's business as it relates to
                 the technology being licensed to the Company, to the Knowledge
                 of Founder 1 without having conducted any infringement
                 analysis, has not infringed, misappropriated or conflicted with
                 and does not infringe, misappropriate or confilct with any
                 intellectual property right of other Persons; (iv) Neither the
                 Company nor Founder 1 has received any notices of, any
                 infringement or misappropriation by, or conflict with, any
                 third party with respect to such intellectual property rights
                 (including, without limitation, any demand or request that the
                 Company or Founder 1 license any rights from a third party)
                 nor, to the Company's or Founder 1's knowledge, are there valid
                 grounds for any such assertion of infringement,
                 misappropriation or conflict; (v) to the best of the Company's
                 and Founder 1's knowledge, the intellectual property rights
                 owned by or licensed to the Company have not been infringed,
                 misappropriated or conflicted by other persons or entities; and
                 (vi) Founder 1 has taken all actions reasonably necessary to
                 maintain and protect the Intellectual Property Rights which
                 they own.

      Each service provider of Founder 1 has executed a proprietary information
      and inventions agreement that provides for the confidential treatment of
      the intellectual property rights of Founder 1 and the assignment to
      Founder 1 of inventions developed in connection with the performance of
      services for Founder 1, in the form previously furnished or made available
      to the Investors.  To the Founder 1's best knowledge, no such service
      provider is in violation thereof.  To Founder 1's best knowledge, all
      relevant technology has been assigned to Founder 1 by all service
      providers. Each service provider of the Company will execute a proprietary
      information and inventions agreement that provides for the confidential
      treatment of the intellectual property rights to be held by the Company
      and the assignment to the Company of inventions to be developed in
      connection with services performed for the Company.

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                                      -16-


      3.    The Founders declare that since the acquisition of the shares by the
            Founders, the Company did not and does not engage in any anti-
            competition violations  which could have a considerable influence on
            the profitability and the longevity of the Company.

      4.    The Company possesses or is applying for all essential official
            approvals and licenses, which are necessary for the management of
            the present business enterprise. The Company has not infringed on
            the rights of third parties or governing law including competition
            laws, commercial business laws, and the provisions of environmental
            protection since the acquisition of the shares by the Founders. In
            the past, the business enterprise has also not infringed on any
            provisions which serve to protect the environment.

      5.    To the best of the Founders' knowledge, the Company owns or has
            entered into agreements to provide it with the production and
            procedural know-how as well as all related documents to develop and,
            if necessary, to produce and to sell products.

      6.    To the best of the Founders' knowledge, there are no special
            circumstances which could significantly impair the business of the
            Company in the future.

      7.    Annex 7 of this Agreement contains a complete and correct list of
            all bank accounts of the Company and all powers granted to employees
            for the respective bank accounts.

      8.    Claims for compensation by an employee as an inventor have not been
            submitted to the management since the acquisition of the shares by
            the

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                                      -17-


            Founders. To the best of the Founder's knowledge, the Company
            does not use any inventions made by employees other than those to
            which it holds title or valid license rights.

      9.    The Company has not yet established an advisory council.

      10.   The Company has not been a party to continuing or threatened
            lawsuits, arbitration proceedings, tax proceedings, administrative
            proceedings, or investigations since the acquisition of the shares
            by the Founders. Since this point in time, the Company has not been
            subject to any judgements, administrative acts or the like which
            would significantly interfere or limit specific business measures
            for the acquisition or transfer of assets, for competition, or for
            the management of the business enterprise. To the best of the
            Founders' and the Company's knowledge, the Company is not delayed in
            performance of any contractual or legal obligations to the current
            day.

      11.   Annex 8 of this Agreement contains all obligations to third parties
            (e.g. banks, leasing companies, lessors) worth more than DM 50,000
            (fifty thousand German marks) per annum which were entered into or
            granted with the exception of those concerning employment
            relationships.

      12.   As long as nothing else is revealed by this Agreement, the Company
            has delivered all tax returns and all other legally necessary
            declarations to the public authorities by the deadline or within an
            explicit or implicit extension. The Company has paid all taxes,
            prepayment of taxes, and other compulsory public charges due and
            withheld all taxes to be withheld, social insurance contributions,
            and other compulsory public charges. The Company delivered and/or
            paid the foregoing to the re-

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                                      -18-

            spective recipients within the deadline including all related late
            penalties and fines.

      13.   With the exception of the contracts mentioned explicitly in this
            Agreement including its annexes, particularly the enclosed contracts
            made with the Founders (annex 11, 12, 14 - 16), in particular the
            Company is not a party to contracts of the following kind:

            -  contracts or other settlements with the Founders, their
               relatives, dependent enterprises, or former shareholders;

            -  contracts with third parties relating to the acquisition of a
               share in the Company or similar rights of third parties;

            -  tenancy agreements, leases, and leasing contracts with a value of
               more than DM 50,000 (fifty thousand German marks) per annum
               with the exception of the usual contracts for equipment for
               utilities, office furnishings, automobiles and operating
               equipment ;

            -  other contracts which individually or together establish an
               obligation exceeding DM 100,000 (one hundred thousand German
               marks) per annum and with whose fulfillment no party had yet
               begun at the time of concluding this contract with the
               exception of such contracts which have been concluded in the
               normal course of business;

            -  agreements concerning the purchase or sale of items from the
               fixed assets or construction contracts with a value of more
               than DM 50,000 (Fifty Thousand German marks);

            -  commission agreements or the like in connection with the existing
               shareholdings;

            -  contracts which could significantly impair the Company in its
               business conduct or in its freedom of competition;

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                                      -19-


            -  collective or Company-specific collective employment agreements.

      14.   The Company is in compliance with (a) the terms of its Articles of
            Association, by-laws or other charter or organizational documents,
            (b) all Contracts to which the Company is a party or by or to which
            any of them or their assets or Properties may be bound or subject,
            (c) all applicable laws, statutes, ordinances, rules, regulations or
            other legal requirements, whether federal, state, local or foreign,
            and (d) all applicable orders, writs, judgements, injunctions,
            awards and decrees of any court, other governmental entity or
            arbitrator except, in the case of (b) and (c), such failures to
            comply as would not have a material adverse effect. The Company has
            not received any written or oral notice of any violation by the
            Company of, or default by the Company under, any of the items
            described in clauses (a) through (d) above in this paragraph.
      15.   No consent, approval, order or authorization of, or registration,
            qualification, designation, declaration or filing with, any
            governmental authority is required on the part of the Company in
            connection with the execution and delivery of this Agreement, the
            offer, issuance, sale and delivery of the capital stock of the
            Company, or the other transactions to be consummated in connection
            with this Agreement, except such filings as have been made prior to
            and shall be effective before the execution of this Agreement by the
            Company.

                                     Part 3
                                     ------
                                     (S) 4
                                   Liability

1.    In case of a violation of assurances or warranties within the meaning of
      (S) 3 of this Agreement, the Founders , as co-debtors (debtors jointly and
      severally li-

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                                      -20-


      able) with regard to the Investor and the Company, are obligated to
      replace the full damage to the Company or the proportionate damage to the
      Investors, even insofar as the damage only affects the Company, upon the
      election of the Investor. Damage is the net worth of the difference
      between the described or guaranteed state of affairs and the actual state
      of affairs or, if the net worth cannot be ascertained, the estimated costs
      for bringing about the described or guaranteed state of affairs. However,
      the liability of the Founders 2-9 jointly is limited to a maximum of DM
      50,000

2.    The regulations of German Civil Code (S) 439 para. 1 and (S) 460 are only
      applicable to defects which are explicitly disclosed in this agreement.
      Moreover the Investor have the right to exercise their rights from this
      agreement independently of the fact that if  they, their organs,
      employees, representatives, advisors or auditors knew or should have known
      of the deficiency where they or their advisors were given a sufficient
      opportunity  for examination. German Civil Code (S) 464 and German
      Commercial Code (S) 377 are not applicable.

3.    Limitation of Liability in Time

      a)    The limitation period for all claims of the Investor and the Company
            based on this agreement runs until two months after the submission
            of the annual report for the financial year of 1999 as far as there
            is no longer statutory limitation period valid for the claim.

      b)    Possible claims in connection with (S) 3 I No. 1- 11 shall expire
            after 10 years.

4.    Rescission ("Wandlung") and resignation ("Rucktritt") are impossible in
      view of the present agreement except on the part of the Investor if a
      statement contained in (S) 3 I Nos. 1-11 is incorrect. The right to avoid
      this Agreement according to (S) 123 German Civil Code remains unaffected.


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                                      -21-


                                     Part 4
                                     ------
                                 New Provisions
                                 --------------
                                     (S) 5
              Articles of Association / Transformation into an AG

1.    The Founders shall change the Articles of Association of the Company in
      accordance with annex 10 by a notarized shareholders' resolution.

2.    The Company will decide to create an Advisory Council numbering six
      members. The first advisory council shall be composed of the following
      people:

                  (advisory council person 1 designated by founder 1, chairman)
                  (advisory council person 2 designated by founder 1)
                  (advisory council person 3 designated by investor)
                  (advisory council person 4 designated by investor)
                  (advisory council person 5, pharma expert)
                  (Prof. Ganten, advisory council person 6)

3.    The Company shall from time to time:

      (i) deliver to the Investor as soon as practicable, but in any event with
      in ninety (90) days after the end of each fiscal year of the Company, an
      income statement for such fiscal year, a balance sheet of the Company and
      a statement of stockholders' equity as of the end of such year, and a
      schedule as to the sources and applications of funds for such year, such
      year-end financial reports to be in reasonable detail and prepared in
      accordance with generally accepted accounting principles;

      (ii) deliver to the Investor within thirty (30) days of the end of each
      month, an unaudited income statement and schedule as to the sources and
      applications of funds and balance sheet for and as of the end of such
      month, in reasonable detail;


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                                      -22-


      (iii) deliver to the Investor as soon as practicable, but in any event
      thirty (30) days prior to the end of each fiscal year, a budget and
      business plan for the next fiscal year, prepared on a monthly basis,
      including balance sheets and sources and applications of funds statements
      for such months and promptly after they are prepared, any other budgets or
      revised budgets prepared by the Company;

      (iv) deliver to the Investor such other information relating to the
      financial condition, business, prospects or corporate affairs of the
      Company as Investor may from time to time request;

      (v) maintain its rights to property, including all intellectual property
      and to its facilities in accordance with the best interests of its
      stockholders;

      (vi) maintain such insurance, including if determined by the Advisory
      Council, key person insurance (especially for Drs. Christoffersen and
      Usman and any other officers of the Company);

      (vii) pay its taxes and other obligations as and when they become due in
      the ordinary course of its business;

      (viii) notify Investor of any material defaults by the Company, of all
      material litigation by or against the Company;

      (ix) conduct its business in compliance with all applicable laws and with
      its Articles of association ("Gesellschaftsvertrag")

      (x) maintain a proper system of internal accounting controls;

      (xi) maintain in full force and effect the License Agreement and the
      Services Agreement between the Company  and Founder 1, subject to the
      Termination provision therein.

4.    The Company commits itself to announce the new Articles of Association
      after the corresponding shareholders` resolution to the Trade Register
      without delay. Possible later changes to the Articles of Association shall
      be effected in accordance with the law and the Articles of Association.


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                                      -23-

                                     (S) 6
     Technology, Know-How, Advisory, Service Agreements and Loan Agreements

1.    The Company has concluded an employment agreement for the position of
      general manager with Dr. Christoffersen and Dr. Potzsch in accordance with
      annex 11.

2.    The Company has concluded individual employment contracts with Mr. Andre
      Hansen  in accordance with annex 12.

3.    The Company has concluded a License Agreement and a Service Agreement with
      the Founder 1 in accordance with annex 14.

4.    The Company has concluded a Service Agreement with the Founder 1 in
      accordance with annex 15.

5.    The Company has concluded a Loan Agreement with the Founder 1 in
      accordance with annex 16.

                                     (S) 7
   Commitment under the Law of Obligations to the New Articles of Association

Even before adoption of the resolution necessitated by the increase of capital
and the change of the Articles of Association, the shareholders are obligated to
observe the interests of the Investor and to maintain the orderly continuation
of the Company. Until the registration of the increase of capital, the Founders
will not resolve to or undertake any distribution of profits.

                                     (S) 8
                                     Costs

All costs of the parties to this Agreement, including reasonable legal fees and
related out-of-pocket expenses, in connection with the conclusion of this
Agreement, the increase of capital, the subscription to the new shares, the
change of the Articles of Association, the


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                                      -24-


application for registration in the Trade Register, and other parts of the
transaction directly concerning the Company's relationships are to be borne by
the Company.

                                     (S) 9
                           Condition of Postponement

This Agreement is subject to the postponement condition that the investors
effectively sign their take-over (assumption) declarations in accordance with
(S) 1 paragraph 3 within two months of the signing of this Agreement.

                                     (S) 10
                               General Provisions

1.    The agreements reached in the term sheet of June 16, 1998, insofar as they
      are regulated in detail in this Agreement including annexes, are rescinded
      with the effectiveness of this Agreement; so that in the future only
      individual points, in particular those in relation to the future
      transformation of the Company into a stock corporation with limited
      liability, shall have effect.

2.    Should any of the provisions of this Agreement prove to be invalid or
      should this agreement contain omissions, the efficacy of the remaining
      provisions shall not be disturbed. In lieu of the invalid provision, the
      valid provision, which comes closest to fulfilling the intended economic
      purpose of the invalid provision, shall be deemed agreed upon. In the case
      of omissions, the provision, which represents the meaning and intention of
      this agreement and would have been agreed to if the parties had been aware
      of it shall be deemed agreed upon.

3.    The validity of this Agreement is not conditional on access to a copy of
      this Agreement signed by all the parties.

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                                      -25-


4.    Alterations and supplements to this Participation Agreement necessitate a
      writing, provided the law does not stipulate a stricter form. The
      requirement of the written form can only be cancelled by a written
      agreement of all parties to this agreement.

5.    Exclusive place of jurisdiction and venue for all disputes in connection
      with the participation created by this agreement is Berlin, insofar this
      is legally permissible.

6.    The annexes to this Agreement are an essential part of it. The headings in
      this Agreement only serve for a better orientation and are of no
      significance for the content and interpretation of this agreement.
      Explanations in a provision or annex of this Agreement are also deemed
      listed for purposes of all other provisions or annexes.

7.    A German and an English version of this Agreement exist. Only the English
      version of this Participation Agreement is binding.

Boulder, August 24, 1998
                --

                               /s/ Larry Bullock
               -------------------------------------------------
                        RIBOZYME PHARMACEUTICALS, Inc.
                                   Founder 1


                          /s/ Ralph E. Christoffersen
               -------------------------------------------------
                         Dr. Ralph Earl Christoffersen
                                   Founder 2


                               /s/ Larry Bullock
               -------------------------------------------------
                               Mr. Larry Bullock
                                   Founder 3

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                                      -26-



                               /s/ Nassim Usman
               -------------------------------------------------
                               Dr. Nassim Usman
                                   Founder 4


                              /s/ James Thompson
               -------------------------------------------------
                              Dr. James Thompson
                                   Founder 5


                               /s/ Alene Holzman
               -------------------------------------------------
                               Ms. Alene Holzman
                                   Founder 6


                              /s/ Thomas Rossing
               -------------------------------------------------
                              Dr. Thomas Rossing
                                   Founder 7


Boston, August __, 1998

BB BIOVENTURES L.P.

By: /s/ Luke Evnin

Name: Luke Evnin

Title: Managing Director

Berlin, August 31 , 1998


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                                      -27-

                               /s/ Jorg Potzsch
               -------------------------------------------------
                               Dr. Jorg Potzsch
                                   Founder 8


                              /s/ Thomas Walther
               -------------------------------------------------
                              Dr. Thomas Walther
                                   Founder 9


                          /s/ Ralph E. Christoffersen
               -------------------------------------------------
                           Atugen Biotechnology GmbH
                                    Company



                                List of Annexes
                                ---------------
                                    to the
                                    ------
                            Participation Agreement
                            -----------------------

Annex 1:         Signed Term Sheet of June 16,1998

Annex 2:         Business Plan in the version of July 30, 1998

Annex 3:         Minutes from the shareholders' meeting of June 10, 1998
                 including the Articles of Association

Annex 4:         Excerpt from the Trade Register


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                                      -28-


Annex 5:         List of Shareholders

Annex 6:         Shareholdings in other Companies Which Are Active in
                 the Field of the Company or a Related Field or Are in a
                 Business Relationship with the Company
Annex 7:         Bank Accounts of the Company

Annex 8:         Obligations of the Company Exceeding  DM 50,000

Annex 9:         List of Employees

Annex 10:        Draft of the New Articles of Association

Annex 11:        Employment Contracts for the General Manager(s)

Annex 12         Employment Contract

Annex 13         Patents and applications for patents of founder 1


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                                      -29-


Annex 14         License Agreement

Annex 15         Service Agreement

Annex 16         Loan Agreement

Annex 17         Rights of Preferred Stock

Annex 18         Letter of Intent (BMBF)

Annex 19         Letter of Intent (Senate of Berlin)

Annex 20         Cap table

Annex 21         Founder 1 Patents and Trademark

Annex 22         List of Existing Licensees


[*] Confidential treatment requested