<PAGE>
                                                                   EXHIBIT 10.24


                              [/\#/\] CERTAIN CONFIDENTIAL INFORMATION CONTAINED
                                  IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN
                                OMITTED AND FILED SEPARATELY WITH THE SECURITIES
                                    AND EXCHANGE COMMISSION PURSUANT TO RULE 406
                                      OF THE SECURITIES ACT OF 1933, AS AMENDED.

                       COLLABORATION AND OPTION AGREEMENT

                                 by and between

                                  MYOGEN, INC.

                                       and

                NOVARTIS INSTITUTES FOR BIOMEDICAL RESEARCH, INC.


<PAGE>



                              [/\#/\] CERTAIN CONFIDENTIAL INFORMATION CONTAINED
                                  IN THIS DOCUMENT, MARKED BY BRACKETS, HAS BEEN
                                OMITTED AND FILED SEPARATELY WITH THE SECURITIES
                                    AND EXCHANGE COMMISSION PURSUANT TO RULE 406
                                      OF THE SECURITIES ACT OF 1933, AS AMENDED.


                       COLLABORATION AND OPTION AGREEMENT

         This Agreement is made this 8th day of October, 2003 (the "Effective
Date") by and between Myogen, Inc. ("Myogen"), a Delaware corporation with
principal offices at 7575 W. 103rd Avenue, Westminster, Colorado 80021, and
Novartis Institutes for BioMedical Research, Inc. ("NIBRI"), a Delaware
corporation with principal offices at 400 Technology Square, Cambridge,
Massachusetts 02139.

                                  INTRODUCTION

         WHEREAS, Myogen is a biotechnology company with expertise and
experience in identifying Targets relating to, and discovering, developing and
commercializing compounds aimed at treating, cardiovascular disease;

         WHEREAS, NIBRI and its Affiliates are interested in developing and
commercializing drugs targeting the Myogen Targets using their expertise in
developing, manufacturing, marketing and selling pharmaceuticals worldwide;

         WHEREAS, both parties desire to enter into a collaboration the
objective of which will be to identify and validate compounds which act on the
Myogen Targets, and thereafter for NIBRI and its Affiliates to have the option
to develop, market and sell certain of those compounds as drugs upon the terms
set forth herein and in a License, Development and Commercialization Agreement
identical in substance to EXHIBIT A hereto;

         NOW THEREFORE, in consideration of the mutual covenants set forth in
this Agreement, and other good and valuable consideration, the parties agree as
follows:

                                    ARTICLE I

                                   DEFINITIONS


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


                Collaboration and Option Agreement - Confidential



<PAGE>

         1.1. "ACTIVE COMPOUND" shall mean any chemical compound that has a
specific, desired therapeutic action on, interaction on, or modulation of a
Myogen Target or a Collaboration Target, and any and all compounds having the
same Active Moiety as such Active Compound, whether a small molecule, protein or
antibody.

         1.2. "ACTIVE MOIETY" shall have the meaning assigned to that term under
21 CFR 314.108(a), as such regulation is in effect on the Effective Date;
namely: "the molecule or ion excluding those appended portions of the molecule
that cause the drug to be an ester, salt (including a salt with hydrogen or
coordination bonds), or other noncovalent derivative (such as a complex, a
chelate or clathrate) of the molecule, responsible for the physiological or
pharmacological action of the drug substance."

         1.3. "AFFILIATE" shall mean, with respect to any Person, any other
Person that, directly or indirectly, by itself or through one or more
intermediaries, controls, or is controlled by, or is under common control with,
such Person. The term "control" means the possession, direct or indirect, of the
power to direct or cause the direction of the management and policies of a
Person, whether through the ownership of voting securities, by contract or
otherwise. Control will be presumed if one Person owns, either of record or
beneficially, at least 50% of the voting stock of any other Person. Such other
relationship as in fact results in actual control over the management, business,
and affairs of a Person shall also be deemed to constitute control; provided,
however, that no Person shall be deemed to exercise control over another Person
solely because the latter relies on the former for a majority of its business. A
Person will be deemed an Affiliate only so long as such ownership or control
relationship continues. In the case of NIBRI, "Affiliates" shall also expressly
be deemed to include the Novartis Institute for Functional Genomics, Inc., and
the Friedrich Miescher Institute for BioMedical Research and their respective
Affiliates.

         1.4. "COLLABORATION COMPOUND" shall mean any new chemical compound
synthesized for the first time or identified for the first time as an Active
Compound in the course of the Research Program, but shall explicitly exclude the
NIBRI Compounds.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 2

<PAGE>



         1.5. "COLLABORATION TARGET" shall mean any Target identified for the
first time in the course of the Research Program or a Development Program.

         1.6. "COLLABORATION TECHNOLOGY" shall mean any Technology that relates
to Collaboration Targets and/or Collaboration Compounds.

         1.7. "COMPOUND" shall mean any Myogen Compound, NIBRI Compound, or
Collaboration Compound and other compounds having the same Active Moiety as a
Myogen Compound, NIBRI Compound, or Collaboration Compound.

         1.8. "CONTROLLED" shall mean, with respect to a Compound, Target, or
Technology, the legal authority or right of a party hereto to grant a license or
sublicense of intellectual property rights to another party hereto, or to
otherwise disclose proprietary or trade secret information to such other party,
without breaching the terms of any agreement with a Third Party, infringing upon
the intellectual property rights of a Third Party, or misappropriating the
proprietary or trade secret information of a Third Party.

         1.9. "CRITICAL ISSUES" shall have the meaning set forth in Section
2.7.2 hereof.

         1.10. "DEVELOPMENT CANDIDATE" shall mean a NIBRI Compound, Myogen
Compound or Collaboration Compound, together with the Myogen Target or
Collaboration Target on which it has therapeutic action, as to which NIBRI
exercises its Option pursuant to Section 4.4 of this Agreement to license for
development in the Field.

         1.11. "DEVELOPMENT PROGRAM" shall mean activities associated with
development of a Development Candidate as specified in the License Agreement.

         1.12. "EFFECTIVE DATE" shall mean the effective date of this Agreement
as set forth on the first page hereof.

         1.13. "FIELD" shall mean the research, treatment, prognosis, diagnosis,
prophylaxis, and monitoring of heart muscle disease.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 3

<PAGE>


         1.14. "FTE" shall mean the equivalent of the work of one Myogen
scientist or other project managerial professional, full time for one year,
which equates to a total of [/\#/\] hours per year of work, on or directly
related to the Research Program, including attendance at relevant scientific
seminars and symposia. FTEs shall include equivalent scientific work in the
Research Program delegated to and carried out by contractors (including Myogen's
academic collaborators) under the general direction of Myogen scientists. The
annual rate per FTE shall be [/\#/\].

         1.15. "GCP" shall mean the current Good Clinical Practice standards for
clinical trials for pharmaceuticals, as set forth in the Food, Drug and Cosmetic
Act and applicable regulations promulgated thereunder, as amended from time to
time, and such standards of good clinical practice as are required by the
regulatory authorities of the organizations and governmental agencies in
countries in which Drug Products (as defined in the License Agreement) are
intended to be sold.

         1.16. "GLP" shall mean the current Good Laboratory Practices
regulations promulgated by the Food and Drug Administration, published at 21 CFR
Part 58, as such regulations may be from time to time amended, and such
equivalent regulations or standards of countries outside the United States as
may be applicable to activities conducted hereunder.

         1.17. "IND" shall mean an application to the Food and Drug
Administration, the filing of which is necessary to commence clinical testing of
Compounds in humans, or the equivalent application to the equivalent agency in
any other country or group of countries.

         1.18. "IN VIVO VALIDATION" means, with respect to a Myogen Compound,
Collaboration Compound or NIBRI Compound, the achievement of physiologically
significant activity in an appropriate in vivo model or models, where the level
of physiological significance and the in vivo model(s) to be used will be
specified by the JSC with respect to High Priority Targets and Low Priority
Targets and by Myogen with respect to Extra-Collaboration Targets.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 4

<PAGE>


         1.19. "JOINT STEERING COMMITTEE" or "JSC" shall have the meaning set
forth in Section 2.4 hereof.

         1.20. "KNOW-HOW" means all Technology other than inventions that are
the subject of Patents.

         1.21. "LICENSE AGREEMENT" shall mean the License, Development and
Commercialization Agreement, identical in substance to EXHIBIT A hereto, to be
executed by Myogen and NIBRI with respect to each Development Candidate.

         1.22. "MYOGEN COMPOUND" shall mean any Active Compound that is
Controlled by Myogen and is identified and/or synthesized by Myogen, its
Affiliates, and/or its external academic collaborators in the Field, except for
any Active Compound that has therapeutic action against both a Myogen Target and
Targets within Myogen's HDAC inhibitor program.

         1.23. "MYOGEN KNOW-HOW" shall mean all Know-How of Myogen or its
Affiliates relating to a Myogen Compound, a Collaboration Compound, a
Collaboration Target, or a Myogen Target or relating to or used in connection
with the Research Program.

         1.24. "MYOGEN PATENTS" shall mean any Patents Controlled by Myogen or
any of its Affiliates relating to the Myogen Targets, Myogen Compounds,
Collaboration Targets, Collaboration Compounds, and methods or reagents used in
identifying, using, developing or manufacturing such Myogen Targets, Myogen
Compounds, Collaboration Targets, and Collaboration Compounds, as applicable. A
list of Myogen Patents is appended hereto as Schedule 1.24 and will be updated
periodically to reflect additions thereto during the course of this Agreement.

         1.25. "MYOGEN TARGET" shall mean any Target Controlled by Myogen and
identified and/or synthesized by Myogen, its Affiliates, and/or its external
academic collaborators in the Field, excluding any Targets within Myogen's HDAC
inhibitor program. A list of Myogen Targets as of the Effective Date is set
forth on Schedule 1.25 appended hereto. Such Schedule


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 5

<PAGE>



1.25 may be updated periodically to reflect additions thereto during the course
of this Agreement.

         1.26. "MYOGEN TECHNOLOGY" shall mean all Myogen Patents and Myogen
Know-How.

         1.27. "NIBRI COMPETITOR" means a Person with annual pharmaceutical
sales of [/\#/\] or more.

         1.28. "NIBRI COMPOUND" shall mean any Active Compound synthesized,
identified, or Controlled by NIBRI and/or its Affiliates.

         1.29. "NIBRI KNOW-HOW" shall mean all Know-How of NIBRI or its
Affiliates relating to a NIBRI Compound, a Collaboration Compound, a
Collaboration Target, or a Myogen Target.

         1.30. "NIBRI PATENTS" shall mean any Patents Controlled by NIBRI or any
of its Affiliates relating to NIBRI Compounds, Collaboration Compounds, Myogen
Targets, Collaboration Targets, and methods or reagents used in identifying,
developing, or manufacturing such NIBRI Compounds, Collaboration Targets, and
Collaboration Compounds, as applicable, as in effect on the Effective Date and
at any time during the term of this Agreement.

         1.31. "NIBRI TECHNOLOGY" shall mean all NIBRI Patents and NIBRI
Know-How.

         1.32. "PATENTS" means all existing patents and patent applications and
all patent applications hereafter filed, including any continuation,
continuation-in-part, division, provisional or any substitute applications, any
patent issued with respect to any such patent applications, any reissue,
reexamination, renewal or extension (including any supplementary protection
certificate) of any such patent, and any confirmation patent or registration
patent or patent of addition based on any such patent, and all foreign
counterparts of any of the foregoing.

         1.33. "PERSON" means any individual, corporation, partnership,
association, joint-stock company, trust, unincorporated organization or
government or political subdivision thereof.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 6


<PAGE>


         1.34. "RESEARCH PLAN" shall have the meaning set forth in Section 2.3.1
hereof.

         1.35. "RESEARCH PROGRAM" shall mean research activities and development
activities undertaken under this Agreement, associated with the identification,
design and development of Targets, Compounds and Development Candidates as
provided herein, including but not limited to: identification and initial
testing of Targets and Compounds; selection of Development Candidates from
Targets and Compounds and preparation for preclinical assessment of those
Development Candidates; formulation and manufacture of Development Candidates
for use in preclinical and clinical studies performed in accordance with GCP;
preclinical animal studies performed in accordance with GLP (or the applicable
equivalent); planning, implementation, administration and evaluation of human
clinical trials performed in accordance with GCP and included in Proof of
Concept studies; and manufacturing process development and scale-up as
appropriate at the stage of development encompassed within the Proof of Concept
studies.

         1.36. "RESEARCH PROGRAM COSTS" shall mean extraordinary external
expenses and capital costs that are approved in advance by the JSC and incurred
by or on behalf of a party in connection with the conduct of the Research
Program.

         1.37. "RESEARCH YEAR" means a twelve (12) month period during the term
of a Research Program commencing on October 1 of a given year, and ending on
September 30 of the following year. The first Research Year hereunder shall be
deemed to have commenced on October 1, 2003.

         1.38. "TARGET" shall mean any biological entity identified as being
potentially involved in one or more disease states.

         1.39. "TECHNOLOGY" shall mean all data, technical information,
know-how, experience, inventions (whether or not patented), trade secrets,
processes and methods discovered, developed or applied (with the consent of its
owner) and Controlled by either party or its Affiliates, in connection with
performance by either party under the Research Program, or in connection with
the conduct of a Development Program under the License Agreement, that relate to
the research,


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 7



<PAGE>


development, utilization, manufacture or use of Compounds, Targets, or
Development Candidates, as applicable.

         1.40. "TERRITORY" shall mean [/\#/\].

         1.41. "THIRD PARTY" shall mean any Person that is not a party or an
Affiliate of any party to this Agreement.

         1.42. "WIND-DOWN PERIOD" shall have the meaning set forth in Section
9.4 hereof.

         1.43. "WORK PLAN" shall have the meaning set forth in Section 2.3.2
hereof.

         Capitalized terms used but not otherwise defined herein that are
defined in the License Agreement shall have the meaning ascribed to them
therein.

                                   ARTICLE II

                                RESEARCH PROGRAM

         2.1. COMMENCEMENT.

                  The Research Program shall commence as soon as practicable
after the Effective Date. The Joint Steering Committee shall direct the conduct
of the Research Program and Myogen and NIBRI shall collaborate in the conduct of
the Research Program, with the parties having the roles and responsibilities
specified in the Research Plan and/or applicable Work Plans, all as may be
deemed appropriate by the Joint Steering Committee. The Joint Steering Committee
shall review and coordinate the efforts of the parties with respect to the
Research Program.

         2.2. TERM.

                  The Research Program will conclude three (3) years from the
Effective Date, unless earlier terminated in accordance with the provisions
hereof. Unless earlier terminated in accordance with the provisions hereof, the
Research Program may be extended for an additional



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 8


<PAGE>




term of either one (1) year or two (2) years, in the sole discretion of NIBRI,
upon the provision of written notice to Myogen not later than ninety (90) days
prior to the end of the initial three (3) year Research Program term and,
thereafter, for additional one (1) year periods upon the mutual written
agreement of Myogen and NIBRI prior to the end of the then current Research
Year.

         2.3. RESEARCH PLAN; WORK PLANS.

                  2.3.1. Research Plan, Generally. NIBRI, in consultation with
Myogen, will prepare an overall research plan (the "Research Plan") for the
Research Program. An initial outline of the Research Plan shall be attached to
this Agreement as Schedule 2.3.1. A final version of the Research Plan will then
be submitted to the Joint Steering Committee for approval at the first meeting
of the Joint Steering Committee. The Research Plan will be revised, updated and
submitted to the Joint Steering Committee at least semi-annually for its review
and comment.

                  2.3.2. Work Plans. Within thirty (30) days of the Effective
Date, the parties will agree upon an initial work plan (a "Work Plan")
identifying: (a) priorities with respect to programs, Targets, and compounds
("Projects") to be pursued; (b) the responsibilities of each party with respect
to the same; (c) the appropriate resources of each party to be committed to the
Projects; and (d) developmental milestones, performance criteria, and timeframes
with respect to such Projects. The Work Plan shall be submitted for approval at
the first meeting of the JSC. It is anticipated that the number of Projects
selected for the Work Plan will be no less than three (3) at any time during the
collaboration, unless otherwise agreed to by the parties.

                  2.3.3. Plan Review. The Research Plan and all Work Plans will
be reviewed as necessary at each meeting of the Joint Steering Committee, and at
any other time upon the request of either party, and shall be modified as
appropriate to reflect material scientific or commercial developments. Any
disagreements between the parties with respect to modification of the Research
Plan or a Work Plan will be resolved in accordance with Section 2.7 of this
Agreement.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 9


<PAGE>


                  2.3.4. Research Diligence. Each of Myogen and NIBRI shall work
diligently and shall use commercially reasonable efforts to fulfill its
respective obligations under the Research Plan and any Work Plan.

                  2.3.5. Submission of Reports. Upon achieving the developmental
milestones specified in a Work Plan with respect to a particular Project, Myogen
and NIBRI will complete and present to the JSC a report containing detailed
summaries of the data for the Project specified in the Work Plan.

         2.4. JOINT STEERING COMMITTEE.

                  Upon execution of this Agreement, Myogen and NIBRI will
establish a Joint Steering Committee ("JSC"), which shall consist of an equal
number of executives or scientists as may be designated by each party from time
to time. The JSC shall initially have six (6) members. If the JSC chooses to
designate a Committee Chair, the Chair will be appointed from among the members
of the JSC designated by NIBRI. The JSC shall hold its first meeting within
thirty (30) days of the Effective Date. Thereafter, the JSC shall meet
quarterly, or with such other frequency as may be established by the JSC (but in
no event less often than three (3) times per year), and at such time and
location as may be established by the JSC, for the following purposes:

                  (a)   Provide general oversight of the entire collaboration
                        between Myogen and NIBRI, including the Research Program
                        and any development and commercialization of a
                        Development Candidate under the License Agreement;

                  (b)   Periodically review the overall goals and strategy of
                        the Research Program;

                  (c)   Prioritize the allocation of resources dedicated to the
                        Research Program;

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 10

<PAGE>


                  (d)   Resolve any disagreement between the parties with regard
                        to a particular Development Candidate, and discuss and
                        resolve any other relevant issues submitted to it, in
                        accordance with the dispute resolution procedure set
                        forth in Section 2.7 below; and

                  (e)   Address any matters raised under relevant provisions of
                        the License Agreement.

                  The JSC shall have the authority to create project teams for
the Research Program, each of which will meet (via telephone or video conference
or in person) no less frequently than monthly, and which will report to the JSC
on its progress on activities performed on the Research Program. The JSC shall
also have the authority to create additional subcommittees as needed.
Notwithstanding the foregoing, the JSC shall not have the authority to amend or
modify the terms of this Agreement.

         2.5. EXCHANGE OF INFORMATION.

                  2.5.1. Myogen and NIBRI will share information with the JSC,
as soon as it is available, necessary to facilitate mutual understanding of the
status of the Research Program and decision-making in connection therewith.

                  2.5.2. Neither Myogen nor NIBRI shall use Technology disclosed
by the other party (excluding information which is no longer subject to
confidentiality restrictions under Article V by reason of the exceptions set
forth in Section 5.2(a), (b) and (c)) for any purpose, including the filing of
Patent applications containing such information without the other party's
consent (which shall not be unreasonably withheld), other than for carrying out
the Research Program or discharging its responsibilities under the License
Agreement, or as otherwise permitted under the License Agreement.

                  2.5.3. Upon conclusion of the Research Program and subject to
the provisions of Section 2.5.4 and Article V hereof, each party shall disclose
to the other all technical information known to it which constitutes NIBRI
Technology or Myogen Technology, as the case may be.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 11

<PAGE>
                  2.5.4.

                  (a)  Neither party shall be entitled to information from the
                       other party concerning know-how or technology discovered
                       or developed by that party outside the Research Program
                       or a Development Program under the License Agreement
                       (except as otherwise provided in the License Agreement)
                       or otherwise unrelated to research or development of
                       Targets, Compounds or Development Candidates under this
                       Agreement or the License Agreement; except that each
                       party must disclose to the JSC in a timely manner any and
                       all know-how and/or technology which it discovers or
                       develops regarding: (i) the Myogen Targets; (ii) the
                       Collaboration Targets; or (iii) any Collaboration
                       Technology.

                  (b)  Neither party will apply its rights in any Technology or
                       the use thereof (and will use best efforts to prevent its
                       licensees, if any, from applying similar rights acquired
                       by license) to block or impede the use of such Technology
                       as permitted hereunder by the other party or its
                       assignees or licensees.

         2.6. PRIMARY DATA ACCESS.

                  Myogen and NIBRI shall grant each other access to all data
(including, without limitation, all primary data and data contained in
laboratory notebooks) generated in the course of performing its obligations
under the Research Program. Each party shall have the right, at reasonable
intervals and at such party's own expense, to make copies of such data to use
and transfer as permitted hereunder.

         2.7 DECISIONS OF THE JSC; RESOLUTION OF DISPUTES.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 12



<PAGE>


                  2.7.1. The JSC shall make decisions unanimously where
possible, but at least by majority vote. In the event of a deadlock, NIBRI shall
have the deciding vote on all matters other than those addressed in Section
2.7.2.

                  2.7.2. In the event that the JSC is deadlocked as to: (a) any
proposed significant reorientation of the entire Research Program; or (b) any
material change in financial or other resources required to be expended by
Myogen in connection with the Research Program; ("Critical Issues") then the
parties may have the issue resolved in accordance with the dispute resolution
mechanism set forth in Section 11.3 hereof.

                                  ARTICLE III

                                    PAYMENTS

         3.1. SIGNATURE PAYMENTS BY NIBRI.

                  Within thirty (30) days of the Effective Date, NIBRI will make
an initial payment of four million dollars ($4,000,000) to Myogen, of which: (a)
one million ($1,000,000) is in consideration of licenses hereunder; and (b)
three million ($3,000,000) is a reimbursement of Myogen's past investment in
research and development of the Myogen Technology.

         3.2. ADDITIONAL CASH PAYMENT.

                  NIBRI shall make an additional payment of one million dollars
($1,000,000) within thirty (30) days after the first anniversary of the
Effective Date as a reimbursement of Myogen's past involvement in research and
development of the Myogen Technology.

         3.3. STAFFING AND RESEARCH SUPPORT PAYMENTS.

                  NIBRI will pay to Myogen: (a) [/\#/\]. The JSC shall determine
the exact number of FTEs to be funded by NIBRI in any particular Research Year
and the manner in which such FTEs shall be allocated under the Research Program.
Between [/\#/\] FTEs shall be funded by NIBRI in any Research Year in connection
with the Research Program. Any FTEs greater than

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 13

<PAGE>



[/\#/\] require NIBRI's prior approval. The annual rate per FTE shall be
[/\#/\]. The FTEs shall be funded in support of the Research Program under this
Agreement.

                  Payments due for each Research Year shall be made by NIBRI to
Myogen [/\#/\]. All payments shall be made without deduction for withholding or
other similar taxes, in United States dollars to the credit of such bank account
as may be designated by Myogen in writing to NIBRI. Any payments which fall due
on a date which is a legal holiday in the Commonwealth of Massachusetts may be
made on the next following day which is not a legal holiday in the Commonwealth.

                  In the event that NIBRI terminates its participation in the
Research Program pursuant to Section 9.4, it shall nevertheless continue during
the Wind-Down Period to fund: [/\#/\]

         3.4. RECORDS.

                  Myogen shall keep accurate records and books of accounts
containing all data reasonably required for the calculation and verification of
FTEs employed by, or equivalents supplied by, Myogen in accordance with the
Research Plan.

                  At NIBRI's request, Myogen shall make those records available,
no more than once a year, during reasonable working hours, for review by a
recognized independent accounting firm acceptable to both parties, at NIBRI's
expense, for the sole purpose of verifying the accuracy of those records in the
calculation of Research Program FTEs. NIBRI shall use commercially reasonable
efforts to cause the accounting firm to retain all such information in
confidence.

                  In the event of a negative difference between the average
number of FTEs stated to be involved in the Research Program and the number of
FTEs actually employed, the amount previously advanced to Myogen and
attributable to any such negative difference shall be due and payable to NIBRI
without delay. If the negative difference is more than [/\#/\] in any Research

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 14

<PAGE>


Year, then Myogen shall also pay the reasonable costs of the independent
accountant employed by NIBRI in the review. Interest at the rate of [/\#/\] per
month, assessed from the end of the Research Year to which the negative
difference relates, shall be due from Myogen.

         3.5. MILESTONE PAYMENTS.

                  NIBRI shall make milestone payments in accordance with this
Section 3.5: (a) with respect to each Myogen Compound, Collaboration Compound or
NIBRI Compound having an effect on a High Priority Target, as defined below
(whether or not an Option, as defined below, has been exercised), within [/\#/\]
of the achievement of such milestone; and (b) with respect to each Myogen
Compound, Collaboration Compound or NIBRI Compound having an effect on a Low
Priority Target (as to which NIBRI has exercised its Option), payment within
[/\#/\] days of exercise of the Option for all prior milestones achieved. Except
as explicitly set forth below, milestone payments shall be payable only once
with respect to a particular Myogen Compound, Collaboration Compound or NIBRI
Compound, even though that Myogen Compound, Collaboration Compound or NIBRI
Compound may be subsequently developed for indications other than those for
which regulatory approval was initially sought. In the event that a Myogen
Compound, Collaboration Compound or NIBRI Compound fails in development, any
milestone payments previously paid with respect to such Myogen Compound,
Collaboration Compound or NIBRI Compound shall be fully creditable toward the
same milestone due with respect to another Myogen Compound, Collaboration
Compound or NIBRI Compound advanced as a lead Compound in place of the failed
Compound that acts on the same Myogen Target or Collaboration Target. NIBRI may
deduct from any milestone payments otherwise due to Myogen under this Section
3.5 the amount of any withholding and similar taxes required under applicable
law to be withheld from such payments and paid to applicable tax authorities.

                  The schedule below corresponds to an identical schedule in the
License Agreement; payments made pursuant to this Agreement prior to exercise of
an Option shall be treated as payments made under the License Agreement.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 15

<PAGE>



<Table>
<Caption>

                                                               MILESTONE
DEVELOPMENTAL MILESTONE:                                       PAYMENT
------------------------                                       -------
<S>                                                            <C>
Pre-Clinical Milestones:

  o  Validation of high-throughput assays*                      [/\#/\]

  o  In vitro validation of lead compound*                      [/\#/\]

  o  In Vivo Validation of lead compound or use of the          [/\#/\]
     lead compound as a starting point for medicinal
     chemistry and/or SAR exploration*

  o  Completion of Tox/ADME screening and preclinical
     candidate determination*                                   [/\#/\]

Clinical Milestones:

  o  IND filing                                                 [/\#/\]

  o  Initiation of Phase II clinical evaluation                 [/\#/\]

  o  Initiation of Phase III clinical studies                   [/\#/\]

  o  Regulatory filing [/\#/\]                                  [/\#/\]

  o  First regulatory filing [/\#/\]                            [/\#/\]

  o  Regulatory Approval [/\#/\]                                [/\#/\]

  o  First Regulatory Approval [/\#/\]                          [/\#/\]
</Table>


*Criteria for determining the achievement of any Milestone will be established
by the JSC.

                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 16

<PAGE>


                                   ARTICLE IV

                LICENSE, DEVELOPMENT AND COMMERCIALIZATION RIGHTS

         4.1. EVALUATION LICENSE.

                  4.1.1. Myogen hereby grants to NIBRI and its Affiliates a
non-sublicensable (except to the extent required to engage any academic
collaborators or contractors used in connection with the Research Program by
either party) license in the Territory and in the Field, to use and have used
any and all Myogen Technology, Myogen Compounds, Myogen Targets, Collaboration
Targets, and Collaboration Compounds solely for the purpose of performing the
Research Program. The license granted by Myogen is exclusive solely to the
extent provided in Section 4.2.2.

                  4.1.2. NIBRI hereby grants to Myogen and its Affiliates a
non-exclusive license in the Territory, to use and have used any and all NIBRI
Technology, NIBRI Compounds, Collaboration Targets, and Collaboration Compounds
solely for the purpose of performing the Research Program with respect to the
High Priority Targets and to use and have used only Collaboration Technology for
conducting research and development activities within the Research Program on
any Low Priority Targets or Extra-Collaboration Targets.

         4.2. OPTION TO LICENSE.

                  4.2.1. NIBRI shall have the exclusive right (the "Option") to
license any and all Active Compounds, together with their underlying Myogen
Targets or Collaboration Targets, as Development Candidates, for development and
commercialization of products with respect to any and all human or veterinary
health care uses and any and all agricultural uses, under the terms and
conditions set forth in the License Agreement.

                  4.2.2. While the Option is in effect, Myogen will not grant to
any Third Party rights within the Field to Myogen Technology, Myogen Compounds,
Myogen Targets, Collaboration Targets, or Collaboration Compounds nor will
Myogen enter into any


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 17

<PAGE>


collaboration with a Third Party with respect to any of the foregoing. The
latter restriction shall not apply to Extra-Collaboration Targets, as defined
below, or the Active Compounds having a therapeutic effect on such
Extra-Collaboration Targets, if NIBRI's right of first negotiation has lapsed or
failed to result in a completed transaction between Myogen and NIBRI, despite
the good faith efforts of the parties.

         4.3. PRIORITIZATION OF COMPOUNDS.

                  For purposes of this Agreement and the Research Program, the
JSC shall classify all Myogen Targets and Collaboration Targets as follows:

                  4.3.1. High Priority Targets (which may be identified using
Myogen Compounds, NIBRI Compounds, or Collaboration Compounds) are those Myogen
Targets and Collaboration Targets the study of which, and the allocation of
resources to which, the JSC has established as a high priority of the Research
Program. In the case of Active Compounds related to such High Priority Targets:

                  (a)      NIBRI shall make payments with respect to all
                           research milestones in accordance with Section 3.5
                           above, [/\#/\]

                  (b)      [/\#/\] shall be payable; and

                  (c)      NIBRI may exercise its Option to license an Active
                           Compound relating to a High-Priority Target [/\#/\]
                           other than termination for NIBRI's breach under
                           Section 9.3.

                  4.3.2. Low Priority Targets (which may be identified using
Myogen Compounds and Collaboration Compounds) are those Myogen Targets and
Collaboration Targets the study of which, and the allocation of resources to
which, the JSC has determined are not an immediate priority but could prove to
be of importance in the Research Program. Myogen may continue to study such Low
Priority Targets using its own resources. In the case of Active Compounds
related to such Low Priority Targets:


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 18


<PAGE>

                  (a)      [/\#/\] shall be payable so long as a Low Priority
                           Target retains that status;

                  (b)      At any time during the Research Term, but in any case
                           no later than [/\#/\] after In Vivo Validation of an
                           Active Compound in connection with such Low Priority
                           Target, the JSC will elect either to elevate its
                           status to that of a High Priority Target or to lower
                           its status to an Extra-Collaboration Target, as
                           defined below;

                  (c)      NIBRI may elect at any time during the Research Term,
                           but no later than [/\#/\] after In Vivo Validation of
                           an Active Compound in connection with such Low
                           Priority Target, to exercise its Option with respect
                           to the same. In the event NIBRI exercises its Option,
                           payments associated with all previously achieved
                           milestones shall be due and payable within [/\#/\] of
                           execution of the respective License Agreement; and

                  (d)      If NIBRI does not exercise its Option with respect to
                           a Myogen Compound or a Collaboration Compound
                           relating to a Low Priority Target within the [/\#/\]
                           time period set forth in the immediately preceding
                           subsection, then the Low Priority Target shall become
                           an Extra-Collaboration Target.

                  4.3.3. Extra-Collaboration Targets (which may be identified
using Myogen Compounds) are those Myogen Targets the study of which the JSC
determines not to pursue in connection with the Research Program, or which
subsequently become Extra-Collaboration Targets pursuant to Section 4.3.2(d). In
the case of Extra-Collaboration Targets:

                  (a)      Myogen may continue to study such Extra-Collaboration
                           Targets using its own resources, subject to its
                           continued commitment to the resource levels specified
                           in the Work Plans for the High Priority Targets and
                           the periodic review of the JSC;


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 19

<PAGE>
                  (b)      [/\#/\] shall be payable by NIBRI with respect to
                           Active Compounds acting on such Extra-Collaboration
                           Targets; and

                  (c)      In the event that Myogen contemplates collaborating
                           with a Third Party with respect to development and/or
                           commercialization of an Active Compound acting on an
                           Extra-Collaboration Target, Myogen shall give NIBRI
                           written notice of the same. Within [/\#/\] of receipt
                           of such notice, NIBRI shall inform Myogen in writing
                           as to whether it wishes to negotiate in good faith a
                           collaboration between NIBRI and Myogen for the same
                           purposes. If NIBRI so informs Myogen, then the
                           parties shall have [/\#/\] to negotiate a transaction
                           in good faith. If the parties are unable to
                           consummate a transaction within such period (or such
                           longer period as the parties may agree to in
                           writing), then Myogen may enter into a Third Party
                           transaction with respect to the Extra-Collaboration
                           Target. The right of first negotiation set out in
                           this Section 4.3.3(c) shall survive [/\#/\] beyond
                           any early termination of this Agreement under Section
                           9.4 or [/\#/\] after expiration of this Agreement;
                           provided, however, that if any Active Compound or
                           Extra-Collaboration Target is in development at the
                           time of the termination of this right of first
                           negotiation and has not attained In Vivo Validation,
                           NIBRI may extend the right for a period of up to
                           [/\#/\] or until [/\#/\] after In Vivo Validation is
                           achieved, whichever occurs first, by paying to Myogen
                           an option fee of [/\#/\] for each such
                           Extra-Collaboration Target or Active Compound.

         4.4. EXERCISE OF AN OPTION.

                  NIBRI may exercise an Option by delivery to Myogen of written
notice of exercise (an "Exercise Notice") no later than [/\#/\] after the filing
of an IND for the Development Candidate, specifying the Development Candidate as
to which such Option is being exercised. The parties shall then promptly execute
a License, Development and


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 20


<PAGE>

Commercialization Agreement identical in substance to Exhibit A hereto (the
"License Agreement"), the terms of which are incorporated by reference into, and
are a part of, this Agreement, pursuant to which NIBRI will use commercially
reasonable efforts (as defined in the License Agreement), to further develop and
commercialize the Development Candidate. Development of each Development
Candidate shall proceed as soon as practicable after the Option is exercised, in
accordance with the terms of the License Agreement. NIBRI agrees that, during
the term of this Agreement and after termination of this Agreement, it will not
develop and/or commercialize (either by itself or through a Third Party) an
Active Compound that has been selected for research or development in the course
of the Research Program because it has a potential therapeutic effect against
any of the Myogen Targets or Collaboration Targets except under the terms of the
License Agreement.

         4.5. EXPIRATION OF OPTIONS. Options expire as follows:

                  4.5.1 An Option on an Active Compound relating to a High
Priority Target will expire on the first to occur of:

                  (a)      [/\#/\]

                  (b)      [/\#/\]

                  (c)      [/\#/\]

                  4.5.2 An Option on an Active Compound relating to a Low
Priority Target will expire at the first to occur of:

                  (a)      [/\#/\]

                  (b)      [/\#/\]

                  (c)      [/\#/\]

                  (d)      [/\#/\]



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 21

<PAGE>


         4.6. RIGHTS TO DISCONTINUED COMPOUNDS.

                  In the event that NIBRI elects to discontinue any Research
Program with respect to any Myogen Target for which the parties have identified
a NIBRI Compound that acts on such Target, and NIBRI subsequently contemplates
collaborating with a Third Party with respect to development and/or
commercialization of the NIBRI Compound, NIBRI shall give Myogen written notice
of the same. Within [/\#/\] of receipt of such notice, Myogen shall inform NIBRI
in writing as to whether it wishes to negotiate in good faith a license to such
NIBRI Compound within the Field. If Myogen so informs NIBRI, then the parties
shall have [/\#/\] to negotiate a transaction in good faith. If the parties are
unable to consummate a transaction within such period (or such longer period as
the parties may agree to in writing), then NIBRI may enter into a Third Party
transaction with respect to the NIBRI Compound. The right of first negotiation
set out in this Section 4.6 shall survive [/\#/\] beyond any termination of this
Agreement.

                                   ARTICLE V

                                 CONFIDENTIALITY

         5.1. UNDERTAKING.

                  During the term of this Agreement, each party (the "Receiving
Party") shall keep confidential, and other than as provided herein shall not use
or disclose, directly or indirectly, any trade secrets, confidential or
proprietary information, or any other knowledge, information, documents or
materials, owned, developed or possessed by the other party (the "Proprietary
Party"), whether in tangible or intangible form, the confidentiality of which
such Proprietary Party takes reasonable measures to protect, including but not
limited to Collaboration Technology.

                  (a)      The Receiving Party shall take any and all lawful
                           measures to prevent the unauthorized use and
                           disclosure of such information, and to prevent
                           unauthorized persons or entities from obtaining or
                           using such information.



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 22

<PAGE>

                  (b)      The Receiving Party further agrees to refrain from
                           directly or indirectly taking any action which would
                           constitute or facilitate the unauthorized use or
                           disclosure of such information. The Receiving Party
                           may disclose such information to its Affiliates,
                           officers, employees and agents, to authorized
                           licensees and sublicensees, and to subcontractors in
                           connection with the development or manufacture of
                           Compounds or Development Candidates, as applicable,
                           to the extent necessary to enable such parties to
                           perform their obligations hereunder or under the
                           applicable license, sublicense or subcontract, as the
                           case may be; provided, however, that such Affiliates,
                           officers, employees, agents, licensees, sublicensees
                           and subcontractors have entered into appropriate
                           confidentiality agreements for secrecy and non-use of
                           such information which by their terms shall be
                           enforceable by injunctive relief at the instance of
                           the Proprietary Party.

                  (c)      The Receiving Party shall be liable for any
                           unauthorized use and disclosure of such information
                           by its Affiliates, officers, employees and agents and
                           any such sublicensees and subcontractors.

         5.2. EXCEPTIONS.

                  Notwithstanding the foregoing, the provisions of Section 5.1
hereof shall not apply to knowledge, information, documents or materials that
the Receiving Party can conclusively establish:

                  (a)      have entered the public domain without the Receiving
                           Party's breach of any obligation owed to the
                           Proprietary Party;

                  (b)      have become known to the Receiving Party from a
                           source other than the Proprietary Party, other than
                           by breach of an obligation of confidentiality owed to
                           the Proprietary Party; or



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 23

<PAGE>

                  (c)      are independently developed by the Receiving Party
                           without breach of this Agreement, without reference
                           to or reliance upon knowledge, information or
                           materials of the disclosing party as established by
                           written records.

                  In addition, a Receiving Party may, notwithstanding the
obligations of Section 5.1, disclose knowledge, information, documents or
materials that the Receiving Party can conclusively establish:

                  (i)      are permitted to be disclosed by the prior written
                           consent of the Proprietary Party; or

                  (II)     are required to be disclosed by the Receiving Party
                           to comply with applicable laws or regulations, to
                           defend or prosecute litigation or to comply with
                           governmental regulations, provided that the Receiving
                           Party provides prior written notice of such
                           disclosure to the Proprietary Party and takes
                           reasonable and lawful actions to avoid or minimize
                           the degree of such disclosure.

         5.3. PUBLICITY.

                  The parties will agree upon the timing and content of any
initial press release or other public communications relating to this Agreement
and the transactions contemplated herein.

                  (a)      Except to the extent already disclosed in that
                           initial press release or other public communication,
                           no public announcement concerning the existence or
                           the terms of this Agreement or concerning the
                           transactions described herein shall be made, either
                           directly or indirectly, by Myogen or NIBRI, except as
                           may be legally required by applicable laws,
                           regulations, or judicial order, without first
                           obtaining the approval of the other party and
                           agreement upon the nature, text, and timing of such
                           announcement, which


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 24

<PAGE>

                           approval and agreement shall not be unreasonably
                           withheld.

                  (b)      The party desiring to make any such public
                           announcement shall provide the other party with a
                           written copy of the proposed announcement in
                           sufficient time prior to public release to allow such
                           other party to comment upon such announcement, prior
                           to public release.

         5.4. SURVIVAL.

                  The provisions of this Article V shall survive the termination
of this Agreement.

                                   ARTICLE VI

                                   PUBLICATION

         6.1. PUBLICATION.

                  Each of NIBRI and Myogen, and their respective Affiliates,
agree not to publish or publicly present any results, data, or scientific
findings with respect to the Research Program (except in connection with filings
with the Food and Drug Administration or another similar governmental entity)
without the prior written consent of the JSC. In the event of information
already within the public domain, consent shall not be unreasonably withheld if
sought at least thirty (30) days prior to planned submission for publication or
oral presentation. In all other instances during the term of this Agreement,
publication shall be presumed to be impermissible until the JSC shall have
determined, in its sole judgment, that the intellectual property rights of the
parties in such information first shall have been adequately protected, whether
by foreign filing of Patents or otherwise. To the extent that a proposed
publication of any results, data, or scientific findings with respect to the
Research Program is subject to the terms of Myogen's existing license
agreements, sponsored research agreements or material transfer agreements with
the University of Texas Southwestern Medical Center, the University of North
Texas Health Sciences Center or the University of Colorado, the procedure for
publication of such results, data or findings will be as specified in those
agreements.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 25

<PAGE>

                                  ARTICLE VII

                                 INDEMNIFICATION

         7.1. INDEMNIFICATION BY MYOGEN.

                  Myogen will indemnify, defend, and hold NIBRI and its
Affiliates, their respective employees, shareholders, officers and directors and
the successors, heirs and assigns of each of them, harmless against any loss,
damages, action, suit, claim, demand, liability, expense, bodily injury, death
or property damage (a "Loss"), that may be brought, instituted or arise against
or be incurred by such persons to the extent such Loss is based on or arises out
of: (a) the breach by Myogen of any of its covenants, representations or
warranties set forth in this Agreement; or (b) the development or
commercialization of a Development Candidate, but excluding any such Loss that
is caused by [/\#/\]

         7.2. INDEMNIFICATION BY NIBRI.

                  NIBRI will indemnify, defend, and hold Myogen, and its
Affiliates, and their respective employees, shareholders, officers and directors
and the successors, heirs, and assigns of each of them, harmless against any
Loss that may be brought, instituted or arise against or be incurred by such
persons to the extent such Loss is based on or arises out of: (a) the breach by
NIBRI of any of its covenants, representations or warranties set forth in this
Agreement; or (b) the development or commercialization of a Development
Candidate, but excluding any such Loss that is caused by [/\#/\].

         7.3. CLAIMS PROCEDURES.

                  Each Party entitled to be indemnified by the other Party (an
"Indemnified Party") pursuant to Section 7.1 or 7.2 hereof shall give notice to
the other Party (an "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any threatened or asserted claim as to which indemnity
may be sought, and shall permit the Indemnifying Party to


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 26

<PAGE>

assume the sole control of the defense of any such claim or any litigation
resulting therefrom; provided, however:

                  (a)      That counsel for the Indemnifying Party, who shall
                           conduct the defense of such claim or any litigation
                           resulting therefrom, 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 (unless: (i) the employment of counsel by
                           such Indemnified Party has been authorized by the
                           Indemnifying Party; or (ii) the Indemnified Party
                           shall have reasonably concluded that there may be a
                           conflict of interest between the Indemnifying Party
                           and the Indemnified Party in the defense of such
                           action, in each of which cases the Indemnifying Party
                           shall pay the reasonable fees and expenses of one law
                           firm serving as counsel for the Indemnified Party,
                           which law firm shall be subject to approval, not to
                           be unreasonably withheld, by the Indemnifying Party);
                           and

                  (b)      The failure of any Indemnified Party to give notice
                           as provided herein shall not relieve the Indemnifying
                           Party of its obligations under this Agreement to the
                           extent that the failure to give notice did not result
                           in harm to the Indemnifying Party or materially
                           compromise the defense of such claim.

                  (c)      No Indemnifying Party, in the defense of any such
                           claim or litigation, shall consent to entry of any
                           judgment or enter into any settlement, except with
                           the approval of each Indemnified Party (which
                           approval shall not be unreasonably withheld), except
                           a settlement which imposes only a monetary obligation
                           on the Indemnifying Party and which includes as an
                           unconditional term thereof the giving of a release
                           from all liability in respect to such claim or
                           litigation by the claimant or plaintiff to the
                           Indemnified Party.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 27


<PAGE>

                  (d)      Each Indemnified Party shall furnish such information
                           or reasonable assistance regarding itself or the
                           claim in question as an Indemnifying Party may
                           reasonably request in writing and shall be reasonably
                           required in connection with the defense of such claim
                           and litigation resulting therefrom.

         7.4. COMPLIANCE.

                  The parties shall comply fully with all applicable laws and
regulations in connection with their respective activities under this Agreement.

                                  ARTICLE VIII

                          INTELLECTUAL PROPERTY RIGHTS

         8.1. OWNERSHIP.

                  8.1.1. Subject to any licenses explicitly granted under this
Agreement or a License Agreement, each party shall retain its intellectual
property rights in all Technology Controlled by it on the Effective Date or
otherwise arising outside of the Research Program.

                  8.1.2. Any new invention created or any new Know-How generated
exclusively by a party or its Affiliate (directly or through others acting on
its behalf) prior to and during the term of this Agreement shall be owned by
such party; provided, however, that if such new invention or new Know-How of
Myogen is necessary to NIBRI's exercise of its license rights under a License
Agreement, then the definition of Myogen Technology will be deemed to include
such new invention or new Know-How that are included within the licenses granted
to NIBRI under the License Agreement.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 28

<PAGE>

                  8.1.3. Any new invention created jointly by the parties shall
be jointly owned (a "Joint Invention"), and the respective rights of the parties
with respect to the Joint Invention shall be determined in accordance with
United States patent law as it applies to issues of joint ownership of
intellectual property as of the Effective Date.

                  8.1.4. NIBRI will retain ownership of all intellectual
property rights in and to the NIBRI Compounds. Myogen will take all reasonable
actions requested by NIBRI, including execution of appropriate transfer
documents, patent filings and applications for registration, to perfect NIBRI's
ownership interests in and to the NIBRI Compounds.

         8.2. PREPARATION AND COSTS.

                  Myogen shall take responsibility and pay for the preparation,
filing, prosecution and maintenance of all Myogen Patents, and NIBRI shall take
responsibility and pay for the preparation, filing, prosecution and maintenance
of: (a) all NIBRI Patents; (b) any patents and patent applications claiming
Joint Inventions; and (c) all Patents related to Development Candidates. Myogen
shall provide the JSC with periodic reports listing, by name, Myogen Patents
filed in the United States and other jurisdictions, along with a general summary
of the claims made and the jurisdictions of filing. In good time, before the
deadline for foreign filing of any patent application filed in the United
States, Myogen will notify NIBRI whether it intends to foreign file such patent
application, and if it intends to do so, in what countries it proposes to
foreign file. The parties hereby agree that to the extent legally possible and
commercially reasonable, the responsible party shall, at a minimum, prepare,
file, prosecute and maintain patent coverage as described in this section in the
countries listed in Schedule 8.2 hereto. NIBRI and Myogen agree to use all
commercially reasonable efforts to secure patent protection on any intellectual
property created during the Research Program. NIBRI will consult with Myogen on
the drafting and prosecution of patent applications on Joint Inventions that
relate to the Myogen Targets and/or the Collaboration Targets in the United
States and in countries listed in Schedule 8.2 that are commercially viable,
and, to the extent reasonably practicable under the


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 29

<PAGE>

circumstances, give Myogen an opportunity to comment and suggest revisions to
any patent application covering such Joint Inventions.

         8.3. DISCONTINUATION.

                  The party initially responsible under Section 8.2 for the
preparation, filing, prosecution and maintenance of a particular Patent shall
give at least thirty (30) days advance notice to the other party of any decision
to cease preparation, filing, prosecution and maintenance of that Patent in a
jurisdiction listed on Schedule 8.2 hereof. Discontinuation may be elected on a
country-by-country basis or for a Patent application or Patent series in total.
In such case, the other party may elect at its sole discretion to continue
preparation, filing, and prosecution or maintenance of the discontinued Patent
at its sole expense.

         8.4. ADVICE TO JSC ON INTELLECTUAL PROPERTY MATTERS.

                  The JSC shall appoint an intellectual property subcommittee
comprising appropriate legal counsel from each party to advise the JSC on
intellectual property protection issues. Such subcommittee shall report at least
quarterly to the JSC.

                                   ARTICLE IX

                              TERM AND TERMINATION

         9.1. TERM.

                  This Agreement will extend until the termination (including
any early termination hereunder) of the Research Program (including any
extension thereof), unless earlier terminated by either party hereto in
accordance with this Agreement, or unless extended by mutual agreement of the
parties.

         9.2. TERMINATION OF THE RESEARCH PROGRAM BY NIBRI FOR CAUSE.



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 30

<PAGE>

                  Upon written notice to Myogen, NIBRI may at its sole
discretion unilaterally terminate the Research Program and this Agreement upon
the occurrence of any of the following events:

                  (a)      Myogen shall breach any of its material obligations
                           under this Agreement or the License Agreement, and
                           such breach shall not have been remedied or steps
                           initiated to remedy the same to NIBRI's reasonable
                           satisfaction, within sixty (60) days after NIBRI
                           sends written notice of breach to Myogen;

                  (b)      Myogen shall cease to function as a going concern by
                           suspending or discontinuing its business for any
                           reason except for interruptions caused by Force
                           Majeure, strike, labor dispute or any other events
                           over which it has no control; or

                  (c)      Upon a sale, merger, consolidation, transfer, or
                           other reorganization of Myogen in which substantially
                           all of the assets of Myogen are transferred or in
                           which the holders of Myogen's capital stock
                           immediately prior to the transaction hold less than a
                           majority of the capital stock of the surviving entity
                           subsequent to the transaction, in either case to an
                           entity or an Affiliate thereof reasonably conceived
                           by NIBRI to be a NIBRI Competitor.

                  In the event of any valid termination under this Section 9.2,
NIBRI shall not be required to make any payments under Section 3.3 hereof which
are not due and payable prior to receipt by Myogen of the notice of breach
referenced under Section 9.2(a) or receipt by Myogen of the notice of
termination pursuant to Section 9.2(b), as the case may be. Notwithstanding the
foregoing, any License Agreement then in effect shall continue in effect unless
it is expressly terminated in accordance with its terms.

         9.3. TERMINATION OF THE RESEARCH PROGRAM BY MYOGEN FOR CAUSE.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 31

<PAGE>


                  Myogen may at its sole discretion terminate the Research
Program and this Agreement upon written notice to NIBRI upon the occurrence of
any of the following events:

                  (a)      NIBRI shall breach any of its material obligations
                           under this Agreement or the License Agreement and
                           such breach shall not have been remedied or steps
                           initiated to remedy the same to Myogen's reasonable
                           satisfaction, within sixty (60) days after Myogen
                           sends written notice of breach to NIBRI; or

                  (b)      NIBRI shall cease to function as a going concern by
                           suspending or discontinuing its business for any
                           reason except for interruptions caused by Force
                           Majeure, strike, labor dispute or any other events
                           over which it has no control, and no Affiliate of
                           NIBRI shall have assumed NIBRI's function.

                  Upon any termination under Section 9.3(a), all licenses and
other rights (including Options) granted hereunder shall also terminate.
Notwithstanding the foregoing, any License Agreement then in effect shall
continue in effect unless it is expressly terminated in accordance with its
terms.

         9.4. EARLY TERMINATION OF THE RESEARCH PROGRAM BY NIBRI.

                  [/\#/\]


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 32


<PAGE>


         9.5. EFFECT OF TERMINATION.

                  Except where explicitly provided elsewhere herein, termination
of this Agreement for any reason, or expiration of this Agreement, will not
affect: (a) obligations which have accrued as of the date of termination or
expiration; and (b) obligations and rights which, expressly or from the context
thereof, are intended to survive termination or expiration of this Agreement,
including but not limited to obligations of confidentiality under Section 2.5.2,
Article V hereof and the indemnification provisions of Article VII hereof.
Except as otherwise provided hereunder, all licenses granted under this
Agreement shall terminate upon termination or expiration of this Agreement.

                                   ARTICLE X

                         REPRESENTATIONS AND WARRANTIES

         10.1. REPRESENTATIONS AND WARRANTIES OF MYOGEN.

                  Myogen represents and warrants to NIBRI as follows:

                  (a)      AUTHORIZATION. This Agreement has been duly executed
                           and delivered by Myogen and constitutes the valid and
                           binding obligation of Myogen, enforceable against
                           Myogen in accordance with its terms except as
                           enforceability may be limited by bankruptcy,
                           fraudulent conveyance, insolvency, bankruptcy,
                           reorganization, moratorium and other laws relating to
                           or affecting creditors' rights generally and by
                           general equitable principles. The execution, delivery
                           and performance of this Agreement have been duly
                           authorized by all necessary action on the part of
                           Myogen, its officers and directors. No provision of
                           this Agreement violates any other agreement that
                           Myogen may have with any other person or company, and
                           Myogen acknowledges that NIBRI has relied on that
                           representation in entering into this Agreement.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 33

<PAGE>

                  (b)      MYOGEN CONTROLLED RIGHTS. As of the Effective Date,
                           Myogen owns or possesses adequate licenses or other
                           rights to use all Myogen Technology relating to the
                           Myogen Compounds and Myogen Targets and to grant the
                           licenses and perform the obligations contemplated
                           herein, except to the extent that Myogen's agreements
                           with Third Party licensors contain restrictions on
                           further sublicense by NIBRI. The granting of an
                           Option to NIBRI hereunder does not violate any right
                           known to Myogen of any Third Party.

                  (c)      THIRD PARTY PATENTS. Except as disclosed in writing
                           between the parties to this Agreement or their
                           respective agents, as of the Effective Date, to
                           Myogen's knowledge there are no issued patents or
                           pending patent applications that, if issued, would be
                           infringed by the development, manufacture, use or
                           sale of any Myogen Compound or Myogen Target, as
                           applicable, pursuant to this Agreement.

         10.2. REPRESENTATIONS AND WARRANTIES OF NIBRI.

                  NIBRI represents and warrants to Myogen that this Agreement
has been duly executed and delivered by NIBRI and constitutes the valid and
binding obligation of NIBRI, enforceable against NIBRI in accordance with its
terms except as enforceability may be limited by bankruptcy, fraudulent
conveyance, insolvency, bankruptcy, reorganization, moratorium and other laws
relating to or affecting creditors' rights generally and by general equitable
principles. The execution, delivery and performance of this Agreement have been
duly authorized by all necessary action on the part of NIBRI, its officers and
directors. No provision of this Agreement violates any other agreement that
NIBRI may have with any other person or company, and NIBRI acknowledges that
Myogen has relied on that representation in entering into this Agreement.



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 34

<PAGE>
                                   ARTICLE XI

                               DISPUTE RESOLUTION

         11.1. GOVERNING LAW, AND JURISDICTION.

                  This Agreement shall be governed and construed in accordance
with the internal laws of the Commonwealth of Massachusetts.

         11.2. DISPUTE RESOLUTION PROCESS.

                  Except with respect to any matters under the purview of the
JSC pursuant to Section 2.7.1, and except for any claim or controversy relating
to a Critical Issue pursuant to Section 2.7.2 and Section 11.3, in the event of
any controversy or claim arising out of or relating to the legal rights and
remedies of the parties arising out of this Agreement, the parties shall, and
either party may, initially refer such dispute to the JSC, and failing
resolution of the controversy or claim within thirty (30) days after such
referral, the matter shall be referred to the President and Chief Executive
Officer of Myogen and the President and Chief Executive Officer of NIBRI who
shall, as soon as practicable, attempt in good faith to resolve the controversy
or claim. If such controversy or claim is not resolved within sixty (60) days of
the date of initial referral of the matter to the JSC, either party may submit
the dispute to any court of competent jurisdiction for resolution.

         11.3. DISPUTE RESOLUTION PROCESS FOR CRITICAL ISSUES.

                  In the event of any controversy or claim arising out of or
relating to a Critical Issue which the JSC is unable to resolve under Section
2.7.2, the parties shall refer the matter to the President and Chief Executive
Officer of Myogen and the President and Chief Executive Officer of NIBRI who
shall attempt in good faith and using their best efforts to resolve the
controversy or claim within sixty (60) days of the date of initial referral of
the matter from the JSC. If such controversy or claim is not resolved within
sixty (60) days, then Myogen may, at its election, either: (a) accept the final
position of the President and Chief Executive Officer of


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 35

<PAGE>

NIBRI with respect to such matter; or (b) terminate this Agreement on thirty
(30) days' written notice, subject to the provisions of Section 9.5. Section 9.4
shall not apply to any termination of this Agreement by Myogen pursuant to the
immediately-preceding subsection (b).

                                  ARTICLE XII

                            MISCELLANEOUS PROVISIONS

         12.1. WAIVER.

                  No provision of this Agreement may be waived except in writing
by both parties hereto. No failure or delay by either party hereto in exercising
any right or remedy hereunder or under applicable law will operate as a waiver
thereof, or a waiver of any right or remedy on any subsequent occasion.

         12.2. FORCE MAJEURE.

                  Neither party will be in breach hereof by reason of its delay
in the performance of or failure to perform any of its obligations hereunder, if
that delay or failure is caused by strikes, acts of God or the public enemy,
riots, incendiaries, interference by civil or military authorities, compliance
with governmental priorities for materials, or any fault beyond its control or
without its fault or negligence.

         12.3. SEVERABILITY.

                  Should one or more provisions of this Agreement be or become
invalid, then the parties hereto shall attempt to agree upon valid provisions in
substitution for the invalid provisions, which in their economic effect come so
close to the invalid provisions that it can be reasonably assumed that the
parties would have accepted this Agreement with those new provisions. If the
parties are unable to agree on such valid provisions, the invalidity of such one
or more provisions of this Agreement shall nevertheless not affect the validity
of the Agreement


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 36

<PAGE>

as a whole, unless the invalid provisions are of such essential importance for
this Agreement that it may be reasonably presumed that the parties would not
have entered into this Agreement without the invalid provisions.

         12.4. GOVERNMENT ACTS.

                  In the event that any act, regulation, directive, or law of a
country or its government, including its departments, agencies or courts, should
make impossible or prohibit, restrain, modify or limit any material act or
obligation of NIBRI or Myogen under this Agreement, the party, if any, not so
affected, shall have the right, at its option, to suspend or terminate this
Agreement as to such country, if good faith negotiations between the parties to
make such modifications therein as may be necessary to fairly address the impact
thereof, are not successful after a reasonable period of time in producing
mutually acceptable modifications to this Agreement.

         12.5. GOVERNMENT APPROVALS.

                  Each party will use commercially reasonable best efforts to
obtain any government approval required in its country of domicile to enable
this Agreement to become effective, or to enable any payment hereunder to be
made, or any other obligation hereunder to be observed or performed. Each party
will keep the other informed of progress in obtaining any such government
approval, and will cooperate with the other party in any such efforts.

         12.6. EXPORT CONTROLS.

                  This Agreement is made subject to any restrictions concerning
the export of materials and technology from the United States that may be
imposed upon or related to either party to this Agreement from time to time by
the Government of the United States. Furthermore, each of NIBRI and Myogen
agrees that it will not export, directly or indirectly, any technical
information acquired from the other party under this Agreement or any products
using such technical information to any countries for which the United States
Government or any agency



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 37

<PAGE>

thereof at the time of export requires an export license or other governmental
approval, without first obtaining the written consent to do so from the
Department of Commerce or other agency of the United States Government when
required by applicable statute or regulation.

         12.7. ASSIGNMENT.

                  This Agreement may not be assigned or otherwise transferred by
either party without the prior written consent of the other party; provided,
however, that (a) NIBRI may assign this Agreement, without the consent of
Myogen: (i) to any of its Affiliates; or (ii) in connection with the transfer or
sale of all or substantially all of its assets or business or in the event of
its merger or consolidation with another company; and (b) Myogen may assign this
Agreement, without the consent of NIBRI in connection with the transfer or sale
of all or substantially all of its assets or business or in the event of its
merger or consolidation with another Person, provided, however, that any such
transaction in which a NIBRI Competitor acquires all of Myogen's assets or
business or merges with Myogen, NIBRI may terminate this Agreement pursuant to
Section 9.2(c). Any purported assignment in contravention of this Section 12.7
shall, at the option of the nonassigning party, be null and void and of no
effect. No assignment shall release either party from responsibility for the
performance of any accrued obligation of such party hereunder. This Agreement
shall be binding upon and enforceable against the successor to or any permitted
assignees from either of the parties hereto.

         12.8. AFFILIATES.

                  Each party may perform its obligations hereunder personally or
through one or more Affiliates, although each party shall nonetheless be solely
responsible for the performance of its Affiliates. Neither party shall permit
any of its Affiliates to commit any act (including any act or omission) which
such party is prohibited hereunder from committing directly. The use of
subcontractors by either party shall not increase the financial obligations of
the other party hereunder in any respect.


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 38

<PAGE>

         12.9. COUNTERPARTS.

                  This Agreement may be executed in counterparts, each of which
shall be deemed to be original and both of which shall constitute one and the
same Agreement.

         12.10. NO AGENCY.

                  Nothing herein contained shall be deemed to create an agency,
joint venture, amalgamation, partnership or similar relationship between NIBRI
and Myogen and their respective Affiliates. Notwithstanding any of the
provisions of this Agreement, neither party to this Agreement shall at any time
enter into, incur, or hold itself out to Third Parties as having authority to
enter into or incur, on behalf of the other party, any commitment, expense, or
liability whatsoever, and all contracts, expenses and liabilities in connection
with or relating to the obligations of each party under this Agreement shall be
made, paid, and undertaken exclusively by such party on its own behalf and not
as an agent or representative of the other.

         12.11. NOTICE.

                  All communications between the parties with respect to any of
the provisions of this Agreement will be sent to the addresses set out below, or
to such other addresses as may be designated by one party to the other by notice
pursuant hereto, by prepaid, certified mail (which shall be deemed received by
the other party on the seventh business day following deposit in the mails), or
by facsimile transmission, or other electronic means of communication (which
shall be deemed received when transmitted), with confirmation by first class
letter, postage pre-paid, given by the close of business on or before the next
following business day:

                  if to NIBRI, at:

                     Novartis Institutes for BioMedical Research, Inc.
                     400 Technology Square
                     Cambridge, Massachusetts  02139
                     Attention: Robert L. Thompson, Vice President and General
                                Counsel
                     Fax: (617) 871-3354


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 39

<PAGE>

                  with a copy to:

                     Kirkpatrick & Lockhart LLP
                     75 State Street
                     Boston, Massachusetts  02109
                     Attention:  Eileen Smith Ewing, Esq.
                     Fax: (617) 261-3175

                  if to Myogen, at:

                     Myogen, Inc.
                     7575 W. 103rd Avenue
                     Westminster, Colorado  80021
                     Attention: J. William Freytag, President and Chief
                                Executive Officer
                     Fax: (303) 410-6667

                  with a copy to:

                     Cooley Godward LLP
                     380 Interlocken Crescent, Suite 900
                     Broomfield, Colorado  80021
                     Attention: Steven N. Dupont, Esq.
                     Fax: (720) 566-4099


         12.12. HEADINGS.

                  The paragraph headings are for convenience only and will not
be deemed to affect in any way the language of the provisions to which they
refer.

         12.13. AUTHORITY.

                  The undersigned represent that they are authorized to sign
this Agreement on behalf of the parties hereto.

         12.14. ENTIRE AGREEMENT.

                  This Agreement contains the entire understanding of the
parties relating to the


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 40

<PAGE>

matters referred to herein, and may only be amended by a written document, duly
executed on behalf of the respective parties.

         12.15. NOTICE OF PHARMACEUTICAL SIDE-EFFECTS.

                  During the term of this Agreement, the parties shall keep each
other and the JSC promptly and fully informed and will promptly notify
appropriate authorities in accordance with applicable law, after receipt of
information with respect to any serious adverse event (as defined by the ICH
Harmonized Tripartite Guideline on Clinical Safety Data Management), directly or
indirectly attributable to the use or application of a Compound.

         12.16. INVOICE REQUIREMENT.

                  Any amounts payable to Myogen hereunder (except any royalty
payments required to be made under the provisions of Article IV of the License
Agreement) shall be made within thirty (30) days after receipt by NIBRI, or its
nominee designated for that purpose in advance by NIBRI in writing to Myogen, of
an invoice covering such payment.

                            [Signature page follows]


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 41

<PAGE>


                              MYOGEN, INC.

                              By: /s/ J. William Freytag
                                  ----------------------------------------------
                                  J. William Freytag
                                  Title: President and Chief Executive Officer

                              NOVARTIS INSTITUTES FOR BIOMEDICAL
                              RESEARCH, INC.

                              By: /s/ Mark Fishman
                                  ----------------------------------------------
                                  Mark Fishman, M.D.
                                  Title: President and Chief Executive Officer



                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential - Page 42


<PAGE>

                                  SCHEDULE 1.24

                                 MYOGEN PATENTS

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

                                      [/\#/\]





                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


                Collaboration and Option Agreement - Confidential

<PAGE>


                                  SCHEDULE 1.25

                                 MYOGEN TARGETS

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

                                      [/\#/\]







                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


                Collaboration and Option Agreement - Confidential

<PAGE>



                                 SCHEDULE 2.3.1

                                  RESEARCH PLAN

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

                                      [/\#/\]





                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential

<PAGE>


                                  SCHEDULE 8.2

                  LIST OF COUNTRIES REGARDING PATENT PROTECTION

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



[/\#/\]


                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential

<PAGE>


                                    EXHIBIT A

          FORM OF LICENSE, DEVELOPMENT AND COMMERCIALIZATION AGREEMENT

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

  [Filed separately as Exhibit 10.25 to the Registration Statement on Form S-1]






                                         [/\#/\]CONFIDENTIAL TREATMENT REQUESTED


           Collaboration and Option Agreement - Confidential