<PAGE>   1
                                                                   EXHIBIT 10.18

                       TERM SHEET FOR CONTRACT API SUPPLY
                           BETWEEN ALLOS AND HOVIONE


This Term Sheet sets forth the principal terms for a supply agreement (the
"Agreement") [ * ] (the "API") for clinical and commercial use between Allos
Therapeutics, Inc., the customer and developer of the API, a Delaware
Corporation, with its principal place of business in Denver, CO, USA, ("Allos")
and The Hovione Group ("Hovione"), herein represented by Hovione Inter Limited a
Swiss corporation, with its principal place of business in Luzern, Switzerland,
the API manufacturer. The parties shall negotiate in good faith the full and
complete terms of the Agreement, which shall be consistent with those terms set
forth in this Term Sheet, but until such Agreement is fully executed by both
parties neither party shall be obligated to enter into any agreements.

PARTIES:           The parties to the Agreement shall be Allos and Hovione and
                   their successors and permitted assigns.

                   During the Agreement's Term, Hovione shall be Allos' primary
                   API manufacturer and Allos and its affiliates and licensees
                   shall purchase no less than the percentages set forth in this
                   Term Sheet of its [ * ] from Hovione, subject to their supply
                   capacity and conformance with the Agreement.

AGREEMENT          Pre-commercial Supply Phase--includes all activities and API
PHASES             lots manufactured after the effective date of this Agreement
                   and before Allos submits an NDA to FDA for the finished
                   product manufactured from the API.

                   Commercial Supply Phase--includes all activities and API lots
                   manufactured after Allos submits an NDA to FDA for the
                   finished product manufactured from the API.

PROJECT            Each Party shall designate an official contact with full
MANAGEMENT:        authority to represent company on technical and project
                   matters ("Project Managers"), Hovione and Allos (with
                   participation of Hovione's agent) shall hold periodic project
                   management and status meetings. Hovione shall provide Allos
                   with a monthly, written production status report, describing
                   progress on completion of outstanding obligations (e.g.,
                   process development, validation, stability data, production
                   runs, pending corrective actions).

                   The Project Managers shall approve and authorize updates of
                   all Master Batch Records, Validation Protocols & Reports,
                   Corrective Action Plans and Implementation Reports, and
                   Changes to the foregoing.

                   PROJECT SCHEDULE:  Hovione will be kept advised in writing of
                   Allos' intentions and time-lines concerning the NDA filing.
                   Allos shall provide Hovione with written notice of
                   significant time-line changes; shall milestones within the
                   time-line be moved by more than 3 months Hovione must be
                   given at least 6 months written notice where reasonably
                   possible; should Allos be unable to provide such notice
                   Hovione will only be obliged to make a best effect attempt at
                   meeting the new time-line. [ * ] batches will be scheduled
                   with at least 9 months written notice.



Confidential Term Sheet: Ver.02             Page 1                March 25, 1999
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HOVIONE            Hovione shall perform the following, as more fully
OBLIGATIONS:       described in Attachment A.

                   1. Hovione shall manufacture and deliver such quantities of
                   the API as ordered by Allos in accordance with the
                   forecasting and purchase procedures.

                   2. Prior to the Allos NDA submission date, Hovione shall
                   complete the following in time to permit completion and
                   submission of such NDA:

                      o Process scale-up and validation (including, but not
                        limited to, all vendors, equipment, processes,
                        cleaning, facilities, and methods), and revalidation,
                        and be prepared for an FDA and EU PAI;

                      o Successful manufacture and delivery of at least three
                        fully independent validation batches suitable for
                        preparing data for submission to FDA and which shall
                        demonstrate that the process has been successfully
                        validated. Hovione shall provide data to demonstrate
                        no less than 24 months real time bulk stability (at
                        least six months of data shall be available 60 days
                        prior to NDA submission).

                      o Successful characterization and delivery of samples of
                        final API reference standard( amount to be determined).

                   3. Hovione shall be responsible, at its expense, for all
                   ongoing validation and to ensure compliance of its
                   manufacturing facility.

                   4. All regulatory filings on the API will be made and owned
                   by Allos. Hovione, in consultation with Allos, shall
                   prepare at its expense the description of the API
                   manufacturing operations and related information (e.g.,
                   methods validation package, stability, representative data
                   and batch records) as required for inclusion in the filing
                   to FDA and other regulatory authorities (e.g., EU), which
                   will contain all of the manufacturing information. Hovione
                   will assist Allos in the preparation of annual updates and
                   in promptly responding to any questions from regulatory
                   agencies. Hovione shall provide qualified technical
                   representatives to attend meetings and/or teleconferences
                   with FDA and other regulatory authorities as needed.

                   5. [ * ]

                   6. Hovione accepts responsibility for that documentation
                   which is filed at the health authority for which it has
                   prepared the information (this shall be referred to as
                   "Hovione's filing at FDA"). Allos will provide Hovione with
                   a certified true copy of every submission and update that
                   directly addresses the information in Hovione's filing at
                   FDA at least 10 days before its filing at the health
                   authority, for joint approval prior to filing.


Confidential Term Sheet: Ver.02      Page 2                       March 25, 1999

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FORECASTING &      FORECASTING: During the Commercial Supply phase of the term
PURCHASE ORDERS    of this contract, [ * ]

                   PURCHASE ORDERS: During the Pre-commercial Supply phase
                   Allos may place purchase orders with Hovione as per Davos'
                   offer dated 6th May 1998.

                   During the Term of this Agreement, Allos shall place
                   purchase orders for, and Hovione shall not refuse to
                   supply, at least the following percent of Allos' [ * ]:
<TABLE>
                     <S>   <C>                                          <C>
                     (i)   [ * ]

                     (ii)  [ * ]

                     (i)   [ * ]

                     (i)   [ * ]
</TABLE>

                   During the Commercial Supply Phase purchase orders for
                   specific quantities of [ * ] shall be submitted for
                   quarterly quantities 90 days prior to the start of each
                   calendar quarter. Each such purchase order shall be formally
                   accepted by Hovione within 30 days, and shall not be
                   rejected so long as Allos has not materially breached the
                   Agreement and failed to cure such breach following written
                   notice from Hovione. Purchase orders shall be based on the
                   API batch size. Aggregate purchase order quantities for a
                   quarter shall not be less than one half nor more than twice
                   -- of the forecast for the quarter covered by the most
                   recently delivered rolling forecast for that quarter,
                   without Hovione's consent which shall be withheld only for
                   reasonable cause; provided, that Hovione shall use its best
                   efforts to timely supply purchase orders in excess of 200%
                   of the applicable forecast. Deliveries shall be made on the
                   dates specified in the purchase orders and agreed to in the
                   form of an order acknowledgement by Hovione or its agent.

COST:              All the work to be carried out under this Agreement prior to
                   NDA Submission, during the [ * ]

                   After NDA submission, that is during the Commercial Supply
                   Phase, the charge


Confidential Term Sheet: Ver.02      Page 3                      March 25, 1999

<PAGE>   4
                          [ * ]
                          [ * ]
                          [ * ]
                          [ * ]

                    [ * ]

                    [ * ]

                    Hovione shall notify Allos of any process improvements or of
                    any possible patent applications. Hovione shall not seek or
                    assist others in seeking, prosecuting, defending or
                    enforcing any patents related to [ * ] (including any
                    composition of matter containing [ * ]), including any
                    method of its manufacture or use without the approval of
                    Allos.

                    [ * ]

DELIVERY &          All API lots shall be delivered to CIF Allos' designated
ACCEPTANCE          drug product manufacturer location, and accompanied by
                    certificates of analysis and compliance with manufacturing
                    requirements. Upon Allos' request, in-process and finished
                    API test samples shall be sent to Allos' designated test lab
                    for testing prior to shipment of sampled lots. Any costs
                    incurred with special packing requirements or courier
                    services shall be for Allos' account.

                    API lots shall be considered accepted upon successful
                    completion of acceptance testing (which shall be initiated
                    upon delivery), subject to revocation upon determination of
                    any latent defects (e.g., subsequent inspections or audits,
                    stability data, failure investigations). However if the
                    communication of defect or complaint which would be detected
                    by such acceptance testing is received more than 90 days
                    after the airwaybill date, Hovione will be under no
                    obligation to replace the lot. Notwithstanding the
                    foregoing, Allos shall be entitled to rely on the accuracy
                    and validity of Hovione certificates of analysis provided
                    with each delivered lot.

                    At the request of either party, unresolved disputes over
                    conformance of a lot to its specifications will be referred
                    to mutually acceptable referee lab. Such referee lab will
                    rule based on Hovione's filings at the FDA, such ruling will
                    be final. Costs will be for the account of the party at
                    fault. Hovione shall be responsible for no more than the
                    prompt replacement of each rejected non-conforming lot, or
                    at Allos' election


Confidential Term Sheet: Ver.02             Page 4               March 25, 1999
<PAGE>   5
                    refunding the amounts paid or incurred by Allos on account
                    of such rejected batch.

                    Each party is obligated to immediately inform the other of
                    any information that indicates or suggests that delivered
                    lots do not conform to applicable requirements under the
                    Agreement or should not be used.

PAYMENTS &          1. [ * ]
SCHEDULE
                    2. [ * ]

                    3. Hovione or Hovione's agent shall ensure all API lots are
                    delivered free of any liens. Hovione has the option to
                    arrange the invoicing by any company of the Hovione group or
                    by its agent, provided Allos is notified and is in
                    agreement, such agreement not being unreasonably withheld.
                    Any such person seeking payment from Allos shall be subject
                    to all defenses, claims and rights that Allos might have
                    against Hovione. Hovione shall have no set-off rights or
                    remedy against Allos in the event that its agent fails to
                    remit payments received from Allos.

SUPPLY              1. All API manufacture shall occur at Hovione's Loures,
ASSURANCE           Portugal establishment. [ * ]

                    2. Subject to Allos' approval, Hovione may establish
                    alternate API manufacturing operations at its Macau facility
                    under mutually acceptable conditions to be agreed to (e.g.,
                    time and product volume).

                    3. Except where not possible, or not desired by the parties
                    (e.g., cGMP corrective actions), Hovione shall make no
                    change in the API manufacture (as defined in Hovione's
                    filings at FDA, and the applicable Master Batch Records,
                    SOPs, compendia standards) and shall remain in compliance
                    with FDA and EU laws, regulations and guidance documents.
                    Allos may require production of additional safety stock,
                    pending completion of change validation and/or FDA approval.
                    All such changes shall be made in conformance to Allos'
                    change control policy and applicable requirements. The
                    implementation of changes shall be subordinated to Allos
                    authorization in the light of regulatory implications,
                    however Allos (and Allos licensees or other users of [ * ])
                    recognize that change is necessary to enable Hovione to
                    remain efficient and cost-effective and thus shall be fully
                    supportive of the implementation of such changes.

                    4. During the Commercial Phase, Hovione shall, upon Allos'
                    request, maintain a six-


Confidential Term Sheet: Ver.02      Page 5                       March 25, 1999
<PAGE>   6


                    month Safety Stock inventory of all critical raw materials
                    or, if requested by Allos during Commercial Phase, finished
                    API based upon the rolling forecast. In case Hovione if
                    forced to keep in its inventories one or more batches of
                    approved API for a period greater than 180 days beyond what
                    was stated as firm delivery shipping dates in the annual
                    rolling forecast for that quantity of API, Hovione is free
                    to invoice such unshipped batches. Such batches shall be
                    kept in trust for Allos until such time as Allos requests
                    their shipment.

                    5. Should Hovione fail to supply in excess of 5% of the
                    amount of API specified in a purchase order for any reason,
                    including Force Majeure, or conditions occur in which
                    Hovione cannot give satisfactory assurance of supply (e.g.,
                    insolvency, adverse FDA actions, loss of supply). In the
                    event of such a failure to supply, Allos shall (among other
                    remedies, including termination and/or reduction of its
                    purchase obligations) have the right to require technology
                    transfer to Allos or any Allos designated manufacturer, and
                    Hovione shall fully assist with such transfer, and no
                    royalties or any obligation shall be due for such transfer
                    or products manufactured by the contingent supplier.

                    6. The parties agree to cure all material breaches within
                    90 days. If no agreement can be reached within 90 days of
                    notification of a breach, the parties agree to the use of an
                    independent and binding arbitrator. The arbitrator's ruling
                    will be binding on all parties. Allos also shall have the
                    right to cancel this agreement in the event the breach
                    cannot be cured as per the above in addition to such
                    arbitration.

PERFORMANCE         All API lots, and the manufacture and import of such lots,
CRITERIA:           shall fully conform with all of the following (as such
                    requirements are in effect at the time of the Manufacture of
                    the applicable lots):

                    1. Applicable specifications, Master Batch Record
                    procedures, and any description in Hovione's filing at the
                    FDA.

                    2. US applicable laws and regulations, specifically
                    including 21 CFR Parts 11, 207, 210,& 211 and the then
                    current version of the FDA guidance documents pertaining to
                    the manufacture of an Active Pharmaceutical Ingredient) and
                    the then current USP/NF requirements.

                    3. Applicable requirements established for the manufacture
                    and supply of the API for the European Union and Japan,
                    including those under statute, regulation and pharmacopoeia.

                    4. All other laws and regulations applicable to the
                    operations of Hovione.

                    5. Hovione shall  successfully pass FDA PAI and all other
                    regulatory inspections carried out by FDA and other
                    regulatory authorities, and Allos audits, without material
                    objection. Except as specifically permitted in Hovione's
                    filing at FDA, Hovione shall not carryout any reworking,
                    in-process or batch blending (including recrystallization or
                    recycling of mother liquors or solvents) or reprocessing
                    without


Confidential Term Sheet: Ver.02       Page 6                      March 25, 1999
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                   prior written authorization from Allos, and shall promptly
                   inform Allos of all OOS events, and provide it with the
                   applicable investigation report and corrective action plans
                   prior to release of the in-process or finished lots that are
                   subject to the OOS event (including related lots).

INSPECTIONS &      Hovione will permit and cooperate with inspections of all
AUDITS:            relevant Hovione facilities, equipment, materials,
                   personnel, operations, records relating to the services
                   performed under the Agreement by representatives of Allos,
                   FDA, and other US and foreign authorities. Allos full-time
                   employees and appointed experts may be present during any or
                   all parts of manufacturing activities. Hovione will provide
                   Allos with immediate notice of any inspections by FDA or
                   other authorities as the inspection pertains to Hovione's
                   manufacture of, or its ability to manufacture, the API.
                   Where possible, Allos full-time employees or a consultant to
                   the Allos Manufacturing or Quality Control Units will have
                   the right to be present for such inspections, and will in
                   all cases be provided a copy of any inspection reports or
                   communications from such inspectors or regulatory
                   authorities, and to review and comment on any planned
                   response by Hovione.

                   During the Commercial Phase Allos may have up to two
                   representatives of its Manufacturing or Quality Control
                   Unit, and its appointed experts, present for and observe any
                   manufacturing operations related to the API, and may conduct
                   two complete quality assurance audits each year during the
                   performance of manufacturing operations, upon 60 days prior
                   notice, and additional audits (with no fewer than 5 days
                   notice) upon the occurrences of any product problems, or
                   changes in manufacturing equipment, facilities or
                   operations. Allos will provide a clear identification of the
                   individuals it wishes to have present at Hovione facilities;
                   Hovione may reasonably refuse entry to individuals, other
                   than the Allos Directors of Manufacturing, Operations or
                   Quality Assurance, that it reasonably believes are present
                   for reasons other than a quality function.

                   Allos will have access to DUNE for review of analytical and
                   batch data in real-time. Allos shall be provided with copies
                   of all documentation related to process deviations and
                   out-of-specification or out-of trend results, and their
                   investigation and corrective actions proposed by Hovione.
                   During audits to Hovione's facilities Allos is entitled to
                   review all documentation that is usually made available to
                   an FDA inspector, in at least an equivalent manner.

                   There shall be no charge for any inspections or audits, and
                   Hovione shall cooperate with both providing of reasonable
                   space for review of documents and assistance of key
                   personnel. Allos representatives, when present at a Hovione
                   site, shall at all times comply with Hovione's internal
                   policies.

INTELLECTUAL       Allos shall exclusively own and have the full right to use,
PROPERTY RIGHTS:   assign and sublicense inventions, process improvements and
                   analytical methods developed under this Agreement that
                   relate to the use, manufacture or testing of [ * ], whether
                   patentable or not; provided, that during the term of this
                   Agreement Hovione shall be entitled to receive good
                   consideration for the use by others of its Know-how as set
                   forth below. Such consideration shall only be due if Hovione
                   is not in breach of this


Confidential Term Sheet: Ver. 02     Page 7                       March 25, 1999
<PAGE>   8
                   Agreement, and Allos shall not authorize more than three
                   parties at any one time (other than Allos) to use such
                   improvements. Allos, with the consultation of Hovione, shall
                   control decisions on patent prosecution, defense and
                   enforcement, and Hovione at Allos' expense, shall reasonably
                   assist Allos in such prosecution, defense and enforcement.

                   Hovione shall have the right to use (but not sublicense or
                   disclose) generically applicable process improvements and
                   analytical methods; provided that such process improvements
                   or analytical methods shall not be used to manufacture or
                   test RSR13 or chemically related compounds covered by US
                   patents (or patent applications) owned by or exclusively
                   licensed to Allos (collectively the [ * ]) for any person
                   other than Allos until the end of all of the following three
                   periods (the "Exclusivity Period"):

                         (i)  The life of the U.S. and EU patents for the [ * ]
                         Compounds (including any term extensions and non-patent
                         market exclusivity periods); and

                         (ii)  Five years from the approval of the FDA NDA of
                         [ * ]; and

                         (iii) The number of years during which Hovione supplied
                         Allos with at least 65% of any of its annual
                         Pre-Commercial or Commercial Supply requirements, plus
                         24 months.

                   Except as directed by Allos, neither Hovione, nor any of its
                   affiliates shall manufacture [ * ], or any other [ * ]
                   Compounds, during the term of the Agreement and the
                   Exclusivity Period.

CONSIDERATION      In order to provide Hovione with an incentive to explore
FOR HOVIONE        patent opportunities and process improvements; and in order
KNOW-HOW           to assure that Hovione acts in the best interests of Allos
                   and its other manufacturers Hovione will be entitled, for as
                   long as it is not in breach of contract, to good
                   consideration as follows:

                   o  [ * ]

                   [ * ]

CONFIDENTIALITY:   Each party shall agree to be bound by obligations of
                   confidentiality, non-use and non-disclosure of the
                   confidential and proprietary information of the other
                   parties, subject to rights under the Agreement. The terms of
                   the confidentiality agreement dated 7th July 1998 shall be
                   deemed to be included in the Agreement. The period during
                   which the obligations of confidentiality shall continue shall
                   be extended to endure for ten years from the return of the
                   other party's confidential information that is in its
                   possession, so long as such information remains confidential


Confidential Term Sheet: Ver. 02     Page 8                       March 25, 1999
<PAGE>   9
                    information.

UNINTERRUPTED       During the validity of this agreement Hovione is obligated
SUPPLY AND FIRST    to assure that Allos has an uninterrupted supply of API:
REFUSAL RIGHT
                    o  To this end Allos assures that it will offer to Hovione a
                       right of first refusal for its requirements beyond the 30
                       tonnes/year amount. This right of first refusal shall
                       only apply to the 65% of the annual demand which exceeds
                       30 tonnes. Hovione may exercise this right in its
                       entirety or in part, and must do so at a competitive
                       price as evidenced by written bids obtained by Allos from
                       equivalent third-parties

                    o  To this end, and in the event that Hovione does not
                       exercise the option as set out above, Hovione is
                       obligated to find alternative sources of API. Hovione
                       must also assure that up-to-date technology is
                       transferred to the alternative supplier(s) as efficiently
                       as possible and that the regulatory process is handled
                       successfully.

                    o  To this end, and in the event that Hovione cannot find
                       alternative sources of API which are acceptable to Allos,
                       Hovione at its expense shall invest in additional
                       capacity to meet all Allos requirements and shall remain
                       the primary supplier of 65% of the API needs for a
                       further 5 years' period at prices to be negotiated in
                       good faith.

TERMINATION:        [ * ]

                    [ * ]

                    [ * ]

                    [ * ]


Confidential Term Sheet: Ver.02          Page 9                 March 25, 1999

<PAGE>   10
                   [ * ]

                   In the event of the Agreement's termination by Allos because
                   of reasons other than Hovione material breach (but not its
                   expiration), Allos, at its election, will either: (i)
                   purchase, at Hovione's documented purchase cost, its raw and
                   in-process materials reasonably purchased for production of
                   [ * ] and that cannot be returned for credit or used for the
                   manufacture products for other customers (subject to the
                   generic competition restriction), plus shipping costs; or
                   (ii) pay for such reasonable raw and in-process materials to
                   be manufactured into API in accordance with the Agreement.
                   Hovione shall inform Allos of the quantities of raw and
                   in-process that Hovione is maintaining in its inventory on a
                   periodic basis (but no less than quarterly). In no event
                   shall Allos be responsible for raw or in-process materials
                   that exceed the amounts that would be required to meet more
                   than API forecasts for six months following the date of
                   termination.

                   Indemnification, intellectual property and other applicable
                   obligations shall survive termination and expiration of the
                   Agreement.

INSURANCE:         Hovione is not required to carry any product liability
                   insurance, but shall carry such other standard insurance as
                   mutually acceptable to the parties.

INDEMNIFICATION:   Allos will indemnify, defend and hold Hovione (and their
                   employees, officers and directors) harmless from (i) product
                   liability claims arising from the testing, sale or use of
                   the API or the product manufactured with it, and (ii)
                   infringement claims arising from breach of Allos warranty.
                   Allos obligations shall not include such claims to the
                   extent that they arise from the (i) breach by any Hovione
                   indemnitee of its obligations under the Agreement, or (ii)
                   any negligent or otherwise wrongful act or omission of any
                   Hovione indemnitee.

                   Hovione will indemnify, defend and hold Allos (and its
                   employees, officer and directors) harmless from (i) product
                   liability claims arising from the manufacture of the API to
                   the extent caused by Hovione's breach of any obligation
                   under the Agreement, and (ii) infringement claims arising
                   from breach of Hovione warranty. Hovione obligations shall
                   not include such claims to the extent that they arise from
                   the (i) breach by any Allos indemnitee of its obligations
                   under the Agreement, or (ii) any negligent or otherwise
                   wrongful act or omission of any Allos indemnitee.

                   In the event that it is ruled by arbitration or in a court
                   of law that Hovione was negligent in observing cGMP's or
                   that it manufactured product in a manner that conflicts with
                   that described in Hovione's filings at FDA or the terms of
                   the Agreement, it shall contribute to the costs associated
                   with a recall or with similar damages. However, in no case
                   shall Hovione's total aggregate liability under the
                   Agreement for any recall ever cause it to pay recall costs
                   and similar damages in a total which exceeds the amount of
                   receipts due from Allos in the 12 months periods immediately
                   before the first notification of the issue that led to the
                   liability/recall and the delivery of the batches involved in
                   such recall.


Confidential Term Sheet: Ver.02            Page 10                March 25, 1999
<PAGE>   11

WARRANTIES:         Standard legal, financial, corporate, capability and
                    conflict, Force Majeure, intellectual property and other
                    warranties, including regulatory (including Generic Drug
                    Enforcement Act) and legal compliance, as mutually
                    acceptable to the parties.

                    Allos and Hovione shall each warrant that to the best of its
                    knowledge and belief the manufacture, import, and sale of
                    [ * ] will not infringe any third party patents or other
                    proprietary rights.

                    Hovione shall warrant that it is not using in the
                    manufacture of [ * ] any process or materials covered by any
                    patent owned or licensed to it without Allos' consent.

ASSIGNMENT:         Assignment of the Agreement is permitted subject to a
                    written agreement by the other party.

MISCELLANEOUS:      Standard legal and other provisions as mutually acceptable
                    to the parties. The Agreement and all disputes relating to
                    it shall be interpreted under New York law and enforceable
                    against all of the parties in the courts of New York. The UN
                    Convention on the Sale of Goods shall not apply. Parties
                    shall submit any disputes, not resolved by meeting between
                    senior management, to binding arbitration held in New York
                    or other any location acceptable to the parties.

     ACKNOWLEDGED AND AGREED

     ALLOS THERAPEUTICS, INC.                   HOVIONE INTER LIMITED

     By: /s/ STEPHEN J. HOFFMAN                 By: /s/ GUY VILLAX
        ------------------------------------       ----------------------------
         Stephen J. Hoffman, Ph.D., MD              Guy Villax
         President & Chief Executive Officer        Chief Executive Officer

     Date: 3/25/99                              Date: 3/25/99





Confidential Term Sheet: Ver. 02    Page 11                       March 25, 1999