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                                                                   Exhibit 10.23

                             TAX SHARING AGREEMENT


     This Agreement is entered into as of the 20th day of October, 2000 between
Novo Nordisk of North America, Inc. ("Parent"), a Delaware corporation, on
behalf of the Parent Group (as defined below), and ZymoGenetics, Inc.
("Subsidiary"), a Washington corporation.

                              W I T N E S S E T H:

     WHEREAS, pursuant to the tax laws of various jurisdictions, Subsidiary
presently files a consolidated federal income tax return, as permitted by
Section 1501 of the Internal Revenue Code of 1986, as amended (the "Code")),
with members of Parent Group;

     WHEREAS, on the Effective Date (as defined below), Subsidiary will cease to
be a member of the Parent Consolidated Group (as defined below); and

     WHEREAS, Parent and Subsidiary desire to set forth their agreement on the
rights and obligations of Parent and Subsidiary with respect to the handling and
allocation of federal income taxes incurred in taxable periods beginning prior
to the Effective Date and certain other tax matters:

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
hereinafter set forth, the parties agree as follows:

     1.   Definitions

     (a)  As used in this Agreement:

          "Effective Date" shall mean the closing date of the Private Placement.

          "Federal Tax" shall mean any tax imposed under Subtitle A of the Code
     and any related interest or penalty imposed under Subtitle F of the Code.

          "Final Determination" shall mean (i) a "determination" as defined in
     Section 1313 (a) of the Code or execution of an Internal Revenue Service
     Form 870AD, (ii) any final disposition of a tax issue by reason of the
     expiration of a statute of limitations or (iii) the payment of tax by
     Parent with respect to any item disallowed or adjusted by any taxing
     authority where Parent determines in good faith that no action should be
     taken to recoup such payment.
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          "Five-Year Treasury Rate" shall mean, for any date, the rate of
     interest specified in the applicable weekly Federal Reserve Statistical
     Release, H. 15 (519) Selected Interest Rates for such date under the
     category "U.S. government securities; Treasury constant maturities; 5-
     year."

          "Losses" shall mean any damage, liability, loss, cost, expense
     (including all reasonable attorneys' fees and expenses), deficiency,
     interest, penalty, imposition, assessment or fine.

          "Parent Consolidated Group" shall mean Parent and each direct and
     indirect corporate subsidiary, including Subsidiary, that is eligible to
     join with Parent in the filing of a consolidated federal income tax return.

          "Parent Group" shall mean, at any time, Parent and each of its direct
     and indirect corporate subsidiaries other than Subsidiary.

          "Post-Effective Date Tax Period" means (i) any tax period beginning
     and ending after the Effective Date and (ii) with respect to a tax period
     that begins before and ends after the Effective Date, such portion of the
     tax period that commences on the day immediately after the Effective Date.
     For purposes of this Agreement, the term "Post-Effective Date Tax Period"
     shall include Subsidiary's taxable year (whether or not such year is a
     short taxable year) which begins at the end of the Effective Date pursuant
     to Treasury Regulations Section 1.1502-76(b)(ii).

          "Pre-Closing Taxes" means (i) all Federal Taxes attributable to
     taxable periods beginning before the Effective Date, to the extent such
     Federal Taxes are attributable to periods (or portions thereof) ending on
     or before the Effective Date, (ii) all state or local income or franchise
     taxes (other than income or franchise taxes imposed by the State of
     Washington or any taxing authority thereof or therein) attributable to
     taxable periods beginning before the Effective Date, to the extent such
     taxes are attributable to transactions occurring on or before the Effective
     Date, and (iii) any liability of Subsidiary under Treasury Regulations
     Section 1.1502-6 or corresponding provision of state, local or foreign law.

          "Pre-Effective Date Tax Period" means (i) any tax period beginning
     before the Effective Date and ending before or on the Effective Date and
     (ii) with respect to a period that begins before and ends after the
     Effective Date, such portion of the tax period ending on and including the
     Effective Date.

          "Prime" shall mean, the rate announced from time to time as "prime" by
     Citibank, N.A., as its prime rate in U.S. dollars.

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          "Private Placement" shall mean the sale by Subsidiary of shares of its
     Series B preferred stock pursuant to the Series B Preferred Stock Purchase
     Agreement made as of October 20, 2000 among Subsidiary, Warburg, Pincus
     Equity Partners, L.P. and the other investors specified therein.

          "Referee" is defined in Section 16.

          "Return" shall mean any tax return, statement, report or form
     (including estimated tax returns and reports, extension requests and forms,
     and information returns and reports) required to be filed with any taxing
     authority.

          "Subsidiary Federal Tax Liability" shall mean, with respect to the
     2000 Short Year (as defined below), the Subsidiary's Federal Tax liability
     for such taxable year, computed as if the Subsidiary were not and never
     were part of Parent Consolidated Group, but rather were filing a separate
     federal income tax return.  Such computation shall be made (A) with regard
     to Subsidiary's (and only Subsidiary's) income, deductions (including net
     operating loss and capital loss deductions), credits (excluding any
     carryforwards of credits) or  similar tax attributes; provided, however,
     that in determining Subsidiary Federal Tax Liability for the 2000 Short
     Year, the amount of Subsidiary's credits that shall be taken into account
     in such determination shall not exceed the amount of Subsidiary's credits
     actually utilized by the Parent Group with respect to FY 2000, (B) as
     though the highest rate of tax specified in subsection (b) of Section 11 of
     the Code (or any other similar rates applicable to specific types of
     income) were the only rates set forth in that subsection, and with other
     similar adjustments as described in Section 1561 of the Code, and (C)
     reflecting the positions, elections and accounting methods used by Parent
     in preparing the consolidated federal income tax return for Parent
     Consolidated Group.

          "Tax Packages" shall mean one or more packages of information, that
     are (i) reasonably necessary for the purpose of preparing Returns of Parent
     Consolidated Group with respect to any Pre-Effective Date Tax Period, or of
     the Subsidiary with respect to any Post-Effective Date Tax Period and (ii)
     completed in all material respects in accordance with the standards that
     Parent has established for its subsidiaries.

          "Tax Proceeding" shall mean any tax audit, dispute or proceeding
     (whether administrative or judicial).

     (b)  Any term used in this Agreement which is not defined in this Agreement
shall, to the extent the context requires, have the meaning assigned to

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it in the Code or the applicable Treasury regulations thereunder or in
comparable provisions of applicable law.

     2.   Administrative and Compliance Matters.

     (a)  Sole Tax Sharing Agreement. Any and all existing tax sharing
agreements or arrangements, written or unwritten, between any member of Parent
Group and Subsidiary shall be terminated as of the Effective Date of this
Agreement.  As of the Effective Date of this Agreement, neither Subsidiary nor
the members of Parent Group shall have any further rights or liabilities
thereunder, and this Agreement shall be the sole tax sharing agreement between
Subsidiary and the members of Parent Group.  Notwithstanding the foregoing, if
any such termination is not binding on any taxing authority, Parent shall hold
Subsidiary harmless against any Losses attributable thereto.

     (b)  Designation of Agent.  Subsidiary hereby authorizes and designates
Parent, as its agent, coordinator, and administrator, for the purpose of taking
any and all actions (including the execution of waivers of applicable statutes
of limitation) necessary or incidental to the filing of any Return, any amended
Return, or any claim for refund, credit or offset of tax or any other
proceedings, and for the purpose of making payments to, or collecting refunds
from, any taxing authority, in each case relating only to Pre-Closing Taxes;
provided, however, that Parent shall not exercise its rights as agent in any
manner that is inconsistent with the rights granted to Subsidiary under this
Agreement, and provided further that nothing in this Section 2(b) shall limit
the rights granted to Subsidiary under this Agreement.  Parent covenants to
Subsidiary that it shall be responsible to see that all such administrative
matters relating thereto shall be handled promptly and appropriately.

     (c)  Pre-Effective Date Tax Period Returns.  Parent will prepare,
consistently with past practice and applicable law and with the assistance of
Subsidiary, the consolidated Federal Tax Returns of the Parent Consolidated
Group for all Pre-Effective Date Tax Periods and FY 2000 (as defined in Section
3 hereof).  Parent shall have the right with respect to such Returns to
determine (i) the manner in which such returns, documents or statements shall be
prepared and filed, including, without limitation, the manner in which any item
of income, gain, loss, deduction or credit shall be reported, (ii) whether any
extensions should be requested, and (iii) the elections that will be made by any
member of Parent Group or Subsidiary.  In addition, subject to Section 8, with
respect to all Pre-Effective Date Tax Periods and FY 2000, Parent shall have the
right to (i) contest, compromise or settle any adjustment or deficiency
proposed, asserted or assessed as a result of any audit of any Return filed by
Parent Consolidated Group, (ii) file, prosecute, compromise or settle any claim
for refund, and (iii) determine whether any refunds to which Parent Consolidated
Group may be entitled shall be received by way of refund or credit against the
tax liability of Parent Consolidated Group.  No later than 60 days after the
Effective Date, Subsidiary shall prepare and

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deliver to Parent Tax Packages that include information of Subsidiary for the
Pre-Effective Date Tax Period that includes the Effective Date.

     (d) Allocation.  Parent and Subsidiary agree (i) to use the "closing of the
books" method (and for avoidance of doubt shall not make a ratable allocation
election) for purposes of allocating Subsidiary's tax items for FY 2000, and
further (ii) that the option amounts payable by Novo Nordisk A/S ("NNAS") to
Subsidiary pursuant to the Option and License Agreement between Subsidiary and
NNAS, dated and effective as of the Effective Date, as amended, shall be
allocated to Subsidiary's Federal Tax periods beginning after the Effective
Date, in each case in accordance with relevant provisions of the Treasury
Regulations Section 1.1502-76.

     (e) Post-Effective Date Tax Period Returns of Subsidiary. Subsidiary shall
be solely responsible for the preparation and filing of its Federal Tax Returns
for all Post-Effective Date Tax Periods and the payment of all Federal Taxes
with respect thereto.

     (f) Other Taxes.  For purposes of the avoidance of doubt, Subsidiary shall
be solely responsible for the preparation and filing of its Returns with respect
to all taxes other than Pre-Closing Taxes, and, except as provided in Section 6,
the payment of all taxes with respect thereto.  For purposes of avoidance of
doubt, Subsidiary shall have no responsibility for (i) the preparation or filing
of any Returns with respect to any taxes of the Parent Group attributable to
Post-Effective Date Tax Periods and (ii) the payment of any such taxes.

Tax Sharing.

     (a)  General.  In accordance with the provisions of this Section 3,
Subsidiary shall pay Parent the sum of (i) for the taxable year of Subsidiary
that ends on the Effective Date (the "2000 Short Year") and is included in the
taxable year of the Parent Consolidated Group that includes the Effective Date
("FY 2000"), an amount equal to the Subsidiary Federal Tax Liability, if any, as
shown on the Pro Forma Return (as defined in paragraph (c) below), and (ii) for
all prior taxable years of Subsidiary in which Subsidiary was included in the
Parent Consolidated Group, $7,400,000 (the "Pre-2000 Federal Tax Amount");
provided, however, that the aggregate amount payable by Subsidiary pursuant to
this Section 3 shall not exceed $27,100,000 (the "Section 3 Maximum Amount").
Subject to this Section 3, Parent and Subsidiary agree that Subsidiary shall
have no further obligations or liabilities to or against Parent in respect of
(i) Pre-Closing Taxes, (ii) any payment contemplated by this Agreement if and
when paid in accordance with the terms hereof, and (iii) any taxes related to a
Post-Effective Date Tax Period.  Parent and Subsidiary further agree that Parent
shall indemnify Subsidiary against all Losses attributable to Pre-Closing Taxes.
Parent shall be entitled to all refunds, if any, received with respect to Pre-
Closing Taxes.

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     (b)  Initial Payment for the 2000 Short Year.  Within 30 days after the
Effective Date, Subsidiary shall pay Parent an amount equal to the sum of (i)
$17,600,000 in respect of the Subsidiary Federal Tax Liability for the 2000
Short Year, and (ii) Pre-2000 Federal Tax Amount.

     (c)  True-up for  the 2000 Short Year.

          (i)  Not later than 30 days prior to the due date (including all
     applicable and valid extensions) for Parent Consolidated Group's Federal
     Tax Return for FY 2000, Parent shall deliver to Subsidiary a pro forma
     Federal Tax return (the "Pro Forma Return") of Subsidiary reflecting the
     Subsidiary Federal Tax Liability, if any, for the 2000 Short Year.  The Pro
     Forma Return shall be prepared in good faith in a manner consistent with
     past practice and using the same methodology as was used in the calculation
     of the estimated Subsidiary Federal Tax Liability for the 2000 Short Year
     set forth in Exhibit A hereto.  The Pro Forma Return shall be delivered
     together with a statement showing a calculation of the amount to be paid
     pursuant to section (3)(c)(ii) below.  Subsidiary shall have the right to
     review and approve (which approval shall not be unreasonably withheld) such
     calculation and Pro Forma Return prior to the filing of the Parent
     Consolidated Group's Federal Tax Return for FY 2000.  If Subsidiary does
     not affirmatively approve or disapprove of such calculation and Pro Forma
     Return within 15 days after the receipt thereof, Subsidiary shall be
     conclusively deemed to have approved of such calculation and Pro Forma
     Return for all purposes of this Agreement.

          (ii)  Subject to approval by Subsidiary of the Pro Forma Return under
     clause (i) hereof, not later than 20 days after the receipt of the Pro
     Forma Return, Subsidiary shall pay to Parent, or Parent shall pay to
     Subsidiary, as appropriate, an amount equal to the difference, if any,
     between (A) the Subsidiary Federal Tax Liability reflected on such Pro
     Forma Return and (B) $17,600,000.

     4.   2000 Short Year Accrued Compensation Deductions.  Subsidiary agrees to
use its best efforts to permit, in accordance with applicable law, the deduction
in the 2000 Short Year of all compensation-related items treated as being
deductible in the 2000 Short Year in the computation of the estimated Subsidiary
Federal Tax Liability set forth in Exhibit A hereto.

     5.   Subsidiary R&D Credits.  Subsidiary shall pay to Parent an amount
equal to the tax benefit from the use in any Post-Effective Date Tax Period
(including but not limited to the use of such credits by means of a carryforward
to a Post-Effective Date Tax Period) of all research credits (within the meaning
of Section 41 of the Code) accrued in Pre-Effective Date Tax Periods (an "R&D
Tax Benefit").  The amount of any such R&D Tax Benefit shall be equal to the
actual reduction in Subsidiary's Federal Tax in any year attributable

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to the use of such credits (or the amount of any refund of tax attributable to
the use of such credits); provided, however, that the aggregate R&D Tax Benefit
(calculated without regard to any interest due with respect to such R&D Tax
Benefit, as described below) shall not exceed $12,000,000. For purposes of this
Section 5, Subsidiary shall be deemed to have realized such R&D Tax Benefit on
the date on which Subsidiary files its Federal Tax Return for the year in which
any such credits are utilized or, in the case of a refund described above, 5
days after the date on which such refund is received. For purposes of
determining the order in which Subsidiary uses credits, the principles of
Sections 38 and 39 of the Code shall apply. Subsidiary shall pay Parent the
amount due under this Section 5 within 30 business days after the date on which
Subsidiary realizes the R&D Tax Benefit of such credits; provided, however, that
no payment shall be due prior to the eighth anniversary of the Effective Date.
The amount of any payment that is deferred during the period prior to the eighth
anniversary of the Effective Date as provided herein shall accrue interest at
the Five-Year Treasury Rate from the date that Subsidiary realizes the R&D Tax
Benefit which created such payment obligation until the date such amount is paid
to Parent. Subsidiary agrees to promptly provide Parent with such information as
Parent may reasonably request with respect to the performance by Subsidiary of
its obligations under this Section 5.

     6.   State of Washington Real Estate Excise Tax.

     Subsidiary agrees to be responsible for, and to pay as and when due, the
full amount of any liability incurred by Subsidiary, Parent or any of the
parties to the Series B Preferred Stock Purchase Agreement in respect of State
of Washington real estate excise tax attributable to the Private Placement, and
will hold harmless and indemnify Parent and each such party against such tax.

     7.   Communication and Cooperation.

     (a)  Consult and Cooperate.  Subsidiary and Parent shall consult and
cooperate fully at such time and to the extent reasonably requested by the other
party in connection with all matters subject to this Agreement.  Such
cooperation shall include, without limitation,

          (i)  the retention and provision on reasonable request of any and all
     information including all books, records, documentation or other
     information pertaining to tax matters relating to Parent Group and
     Subsidiary, any necessary explanations of information, and access to
     personnel, until two years after the expiration of the applicable statute
     of limitation (giving effect to any extension, waiver, or mitigation
     thereof);

          (ii)  the execution of any document that may be necessary or helpful
     in connection with any required Return or in connection with any audit,
     proceeding, suit or action; and

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          (iii)  the use of the parties' best efforts to obtain any
     documentation from a governmental authority or a third party that may be
     necessary or helpful in connection with the foregoing.

     (b)  Provide Information.  Parent and Subsidiary shall keep each other
fully informed with respect to any material development relating to the matters
subject to this Agreement.

     (c)  Tax Attribute Matters.  Parent and Subsidiary shall advise each other
with respect to any proposed tax adjustments relating to a Pre-Effective Date
Tax Period, which are the subject of an audit or investigation, or are the
subject of any proceeding or litigation, and which may affect any tax liability
or any tax attribute of Parent, Subsidiary, Parent Group, or any member of the
Parent Group (including, but not limited to, basis in an asset or the amount of
earnings and profits).  Except as otherwise provided herein, Parent shall
determine the apportionment of tax attributes between Parent Group and
Subsidiary in accordance with applicable laws.  Subsidiary shall have the right
to review and approve of such apportionment (which approval shall not be
unreasonably withheld).  If Subsidiary does not affirmatively approve or
disapprove of such apportionment within 30 days after receipt thereof in writing
from Parent, Subsidiary shall be conclusively deemed to have approved of such
apportionment for all purposes of this Agreement.

     8.   Audits and Contest.

     Notwithstanding anything in this Agreement to the contrary, Parent shall
have full control over any Tax Proceeding relating to Pre-Closing Taxes, and
shall have absolute discretion with respect to any decisions to be made, or the
nature of any action to be taken, with respect to any matter described in this
sentence, provided, however, that Parent shall neither consent nor agree to the
settlement of any such Tax Proceeding if such settlement may affect the tax
liability of Subsidiary, unless Parent has secured the written consent of
Subsidiary to such settlement (which consent shall not be unreasonably
withheld).

     9.   Payments.

     All payments to be made hereunder shall be made in immediately available
funds.  Except as otherwise provided, all payments required to be made pursuant
to this Agreement will be due 90 days after the receipt of notice of such
payment or, where no notice is required, 90 days after the fixing of liability
or the resolution of a dispute.  Payments shall be deemed made when received.
Any payment that is not made when due shall bear interest at a rate equal to
Prime for each day until paid.

     10.  Notices.

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     Any notice, demand, claim, or other communication under this Agreement
shall be in writing and shall be deemed to have been given upon the delivery or
mailing thereof, as the case may be, if delivered personally or sent by
certified mail, return receipt requested, postage prepaid, to the parties at the
following addresses (or at such other address as a party may specify by notice
to the other):

          If to Parent, to:

          Novo Nordisk of North America, Inc.
          405 Lexington Avenue, Suite 6400
          New York, NY 10017-6401
          Attn: Anthony Viceroy, Treasurer
          Fax: 212 867-0298

          If to Subsidiary, to:

          ZymoGenetics, Inc.
          1201 Eastlake Avenue East
          Seattle, WA 98102
          Attn: Shinko Campos,
               Chief Operating Officer
          Fax: 206 442-6608

     11.  Costs and Expenses.

     Except as expressly set forth in this Agreement, each party shall bear its
own costs and expenses incurred pursuant to this Agreement.

     12.  Effectiveness; Termination and Survival.

     This Agreement shall become effective upon the consummation of the Private
Placement.  All rights and obligations arising hereunder with respect to Pre-
Closing Taxes and under Section 6 shall survive until they are fully effectuated
or performed and, provided, further, that notwithstanding anything in this
Agreement to the contrary, this Agreement shall remain in effect and its
provisions shall survive for the full period of all applicable statutes of
limitation (giving effect to any extension, waiver or mitigation thereof).

     13.  Section Headings.

     The headings contained in this Agreement are inserted for convenience only
and shall not constitute a part hereof or in any way affect the meaning or
interpretation of this Agreement.

     14.  Entire Agreement; Amendments and Waivers; Severability.

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     (a)  Entire Agreement.  This Agreement and the exhibits hereto contains the
entire understanding of the parties hereto with respect to the subject matter
contained herein.  No alteration, amendment, modification, or waiver of any of
the terms of this Agreement shall be valid unless made by an instrument signed
by an authorized officer of each of Parent and Subsidiary, or in the case of a
waiver, by the party against whom the waiver is to be effective.

     (b)  Amendments and Waivers.  No failure or delay by any party in
exercising any right, power or privilege hereunder shall operate as a waiver
hereof nor shall any single or partial exercise thereof preclude any other or
further exercise thereof or the exercise of any right, power or privilege.  This
Agreement shall not be waived, amended or otherwise modified except as in
writing, duly executed by all of the parties hereto.

     (c)  Severability.  If any provision of this Agreement or the application
of any such provision to any party or circumstances shall be determined by any
court of competent jurisdiction to be invalid, illegal or unenforceable to any
extent, the remainder of this Agreement or such provision or the application of
such provision to such party or circumstances, other than those to which it is
so determined to be invalid, illegal or unenforceable, shall remain in full
force and effect to the fullest extent permitted by law and shall not be
affected thereby, unless such a construction would be unreasonable.

     15.  Governing Law and Interpretation.

     This Agreement has been made in and shall be construed and enforced in
accordance with the laws of the State of Washington without giving effect to
laws and principles relating to conflicts of law.

     16.  Dispute Resolution.

     If the parties hereto are unable to resolve any disagreement or dispute
relating to this Agreement, including, without limitation, the withholding of
approval by any party under this Agreement, within 20 days, such disagreement or
dispute shall be resolved by a recognized law firm or accounting firm expert in
tax matters in the relevant jurisdiction or that is mutually acceptable to the
parties hereto (a "Referee").  A Referee so chosen shall resolve any such
disagreement pursuant to such procedures as it may deem advisable.  Any such
resolution shall be binding on the parties hereto without further recourse.
Except as otherwise provided herein, the costs of any Referee shall be
apportioned between Parent and Subsidiary as determined by such Referee in such
manner as the Referee deems reasonable, taking into account the circumstances of
the dispute, the conduct of the parties and the result of the dispute.

     17.  Counterparts.

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     This Agreement may be executed in any number of counterparts, each of which
shall be deemed an original, but all of which together shall constitute one and
the same Agreement.

     18.    Assignments; Third Party Beneficiaries.

     Except as provided below, this Agreement shall be binding upon and shall
inure only to the benefit of the parties hereto and their respective successors
and assigns, by merger, acquisition of assets or otherwise (including but not
limited to any successor of a party hereto succeeding to the tax attributes of
such party under applicable law).  This Agreement is not intended to benefit any
person other than the parties hereto and such successors and assigns, and no
such other person shall be a third party beneficiary hereof.

     19.  Further Assurances.

     Parent and Subsidiary shall execute, acknowledge and deliver, or cause to
be executed, acknowledged and delivered, such instruments and take such other
action as may be necessary or advisable to carry out their obligations under
this Agreement and under any exhibit, document or other instrument delivered
pursuant hereto.

     20.  Authorization, etc.

     Each of the parties hereto hereby represents and warrants that it has the
power and authority to execute, deliver and perform this Agreement, that this
Agreement has been duly authorized by all necessary corporate action on the part
of such party that this Agreement constitutes a legal, valid and binding
obligation of each such party and that the execution, delivery and performance
of this Agreement by such party does not contravene or conflict with any
provision or law or of its charter or bylaws or any agreement, instrument or
order binding on such party.

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     IN WITNESS WHEREOF, the parties have executed and delivered this Agreement
as of the day and year first written above.

                    Novo Nordisk of North America, Inc

                    By: /s/ Mads Ovlisen
                       --------------------------
                    Name: Mads Ovlisen
                    Title: President and Chief Executive Officer

                    ZymoGenetics, Inc.

                    By: /s/ Bruce L.A. Carter
                       --------------------------
                    Name: Bruce L.A. Carter
                         ------------------------
                    Title: C.E.O.
                          -----------------------

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