Document:

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                                                                  EXHIBIT 10.20
                                SUPPLY AGREEMENT

         THIS SUPPLY AGREEMENT, made as of the 25th day of August 2000 (the
"Effective Date"), by and between Advanced Magnetics, Inc., a Delaware
corporation having its principal place of business at 61 Mooney Street,
Cambridge, Massachusetts 02138 ("AM"), and Cytogen Corporation, a Delaware
corporation having its principal place of business at 600 College Road East,
Princeton, New Jersey 08540-5380 ("Cytogen").

                                    RECITALS:

         WHEREAS, AM has granted to Cytogen a license to market and sell certain
products on the terms set forth in the License and Marketing Agreement by and
between Cytogen and AM of even date herewith (hereinafter the "Marketing
Agreement");

         NOW THEREFORE, in consideration of the foregoing and of the mutual
covenants and obligations hereinafter set forth, the sufficiency of which is
hereby acknowledged, Cytogen and AM agree as follows:

1.       DEFINITIONS.

         When capitalized, the following terms shall for all purposes of this
Agreement have the meanings specified in this Section.

         1.1 "AFFILIATE" shall mean a Person that directly, or indirectly
through one or more intermediaries, Controls, is Controlled by or is under
common Control with the Person specified. 1.2 "AGENT" shall mean Feridex I.V.,
Combidex and Code 7228, individually or in the aggregate, as the context
provides.

         1.3 "AGENT NET SALES" shall have the meaning set forth in the Marketing
Agreement.

         1.4 "AGENT TECHNOLOGY" shall have the meaning set forth in the
Marketing Agreement.

         1.5 "AGREEMENT" shall mean this document together with all attachments
and exhibits.

         1.6 "AM PROJECTS" shall mean the Combidex Project and the Code 7228
Project, each as defined in the Marketing Agreement.

         1.7 "APPROVED SUBLICENSEE" shall mean any Person sublicensed by Cytogen
with AM's written consent under the terms of this Agreement.

         1.8 "BATCH" shall mean a Lot of approximately 9,000 bottles of Feridex
I.V., Combidex or Code 7228, as the case may be.

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         1.9 "CODE 7228" shall mean the contrast agent currently known as Code
7228, which is composed of the substance AMI-7228.

         1.10 "CODE 7228 APPROVAL DATE" shall mean the later of (a) the date of
AM's receipt of an FDA approval letter permitting commercial marketing of Code
7228 in the United States (said date being referred to as the "Code 7228
Approval Letter Date") and (b) the date on which AM is first able to produce and
provide a supply of Code 7228 to Cytogen for commercial marketing in the United
States in interstate commerce pursuant to and in compliance with an approved NDA
and any other conditions that must be satisfied prior to initial commercial
sales then imposed by law, such supply to be sufficient to supply at least six
months of reasonable Cytogen requirements as set forth in a notice sent to AM by
Cytogen no less than six months after the execution date of this Agreement but
no later than ten (10) business days after AM's receipt of the approval letter
from the FDA and notice thereof to Cytogen. If Cytogen fails to so provide such
notice of supply requirements, the Code 7228 Approval Date shall be the Code
7228 Approval Letter Date.

         1.11 "COMBIDEX" shall mean the contrast agent currently known as
Combidex, which is composed of the substance with the United States Adopted Name
Ferumoxtran-10.

         1.12 "COMBIDEX APPROVAL DATE" shall mean the later of (a) the date of
AM's receipt of an FDA approval letter permitting commercial marketing of
Combidex in the United States (said date being referred to as the "Combidex
Approval Letter Date") and (b) the date on which AM is first able to produce and
provide a supply of Combidex to Cytogen for commercial marketing in the United
States in interstate commerce pursuant to and in compliance with an approved NDA
and any other conditions that must be satisfied prior to initial commercial
sales then imposed by law, such supply to be sufficient to supply at least six
months of reasonable Cytogen requirements as set forth in a notice sent to AM by
Cytogen no less than six months after the execution date of this Agreement but
no later than ten (10) business days after AM's receipt of the approval letter
from the FDA and notice thereof to Cytogen. If Cytogen fails to so provide such
notice of supply requirements, the Combidex Approval Date shall be the Combidex
Approval Letter Date.

         1.13 "COMBIDEX NDA" shall mean the New Drug Application submitted by AM
to the FDA with respect to Combidex and accepted for filing by the FDA on or
about December 21, 1999.

         1.14 "COMMERCIALIZATION" shall mean the distribution by Cytogen of any
Agent for sale in interstate commerce in the U.S.

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         1.15 "CONTRACT QUARTER" shall mean any period of three consecutive
calendar months commencing with the first day of any January, April, July or
October.

         1.16 "CONTRACT YEAR" with respect to any Agent shall mean the twelve
consecutive month period commencing with the first day of the next Contract
Quarter following Commercialization of such Agent, and each consecutive twelve
month period thereafter.

         1.17 "CONTROLS" OR "CONTROL" shall mean, in the case of any Person, the
possession of the power to direct or cause the direction of the management and
policies of such Person, whether through the ownership of at least fifty percent
(50%) of the voting securities thereof or otherwise, and when used in the
context of "Control" of technology or information, shall mean possession by a
Person of the right to grant licenses or sublicenses of such technology, or
disclose such information., without violating the terms of any agreement or
other arrangement with, or the rights of, any other Person or any legally
binding laws or regulations.

         1.18 "CYTOGEN AGREEMENTS" shall mean this Agreement, the Marketing
Agreement and the Escrow Agreement.

         1.19 "CYTOGEN PROJECT" shall mean the Phase III(b) Studies and Phase IV
Studies and any other studies undertaken to enhance the marketing of any Agent
that Cytogen elects to conduct.

         1.20 "DMF" shall mean a Drug Master File as described in 21 CFR
314.420. "Type I DMF" shall mean a DMF which refers to facilities and operating
procedures used to manufacture a drug substance or drug product; "Type II DMF"
shall mean a DMF which refers to drug substances or components used in the
manufacture of a drug substance or drug product.

         1.21 "FDA" shall mean the U.S. Food and Drug Administration of the
Department of Health and Human Services, or any successor agency.

         1.22 "FDCA" shall mean the Federal Food, Drug and Cosmetic Act.

         1.23 "FERIDEX I.V." shall mean the contrast agent commonly known and
marketed as Feridex I.V., which is composed of the substance with the United
States Adopted Name Ferumoxide.

         1.24 "GMPS" shall mean the Current Good Manufacturing Practices
regulations promulgated by the FDA and codified at 21 CFR Parts 210 and 211, as
amended.

         1.25 "LOT" shall mean a batch production run of Agent, or a specific
and identified portion of a batch, having uniform character and quality within
specified limits; or, in the case of a drug product

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produced by continuous process, it is a specific and identified amount produced
in a unit of time or quantity in a manner that assures its having uniform
character and quality within specified limits.

         1.26 "MANUFACTURING TECHNOLOGY" shall mean all proprietary information,
with respect to the manufacture and production of any Agent, including, without
limitation, all trade secrets, technical information, data, techniques,
discoveries, inventions, processes, know-how, improvements, patents (including
any extension, reissue or renewal thereof) and patent applications, that AM now
has or may hereafter conceive, develop, own or Control, which is necessary in
connection with the manufacture of any Agent.

         l.27 "PARTY OR PARTIES" shall mean Cytogen and/or AM, as the context
provides.

         1.28 "PERSON" shall mean an individual, partnership, corporation, joint
venture, unincorporated association, or other entity, or a government or
department or agency thereof.

         1.29 "PHASE III(b) STUDIES" shall mean clinical or other studies of any
Agent which are not necessary for approval of any NDA, but which are begun prior
to approval of an NDA.

         1.30 "PHASE IV STUDIES" shall mean clinical or other studies of Agent
which are undertaken following approval of an NDA, and which are not required to
be conducted as a condition of the FDA approval of an NDA.

         1.31 "PROJECT OR PROJECTS" shall mean the AM Projects and the Cytogen
Project individually or together, as the context provides.

         1.32 "PROJECT INFORMATION" shall mean all information developed as a
result of the Projects, including, without limitation, techniques, discoveries,
processes, copyrights, patents (including any extension, reissue or renewal
thereof) and patent applications, know-how, toxicological and pharmacological
data, clinical trial results, regulatory applications and documents evidencing
approval thereof, and test results, and all information and data provided to a
Party pursuant to Article 6 of the Marketing Agreement.

         1.33 "PURCHASE PRICE" shall mean the purchase price of Feridex I.V.,
Combidex and Code 7228 as set out in Section 2.3, individually or collectively,
as the context provides as the same may be adjusted pursuant to the terms
hereof.

         1.34 "QUALIFIED PERSON" shall mean any employee or agent of Cytogen
engaged in the manufacture of any Agent pursuant to Section 4.1 of this
Agreement, or any employee or agent of AM engaged in the AM Project or the
performance of AM's obligations hereunder, designated by Cytogen or

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AM respectively, to receive Agent Technology or Manufacturing Technology
pursuant to Section 4.3 of this Agreement, who has a need to know the
information included therein and disclosed to them.

         1.35 "QUALIFY" shall mean providing the technological ability to carry
on, and achieving approval from FDA for, the manufacture and packaging of any
Agent.

         1.36 "SPECIFICATIONS" shall mean the written standards established for
the characteristics, quality, and quality control testing of each Agent and its
constituents, components and packaging, which are set forth on EXHIBIT A.

         1.37 "TERM" shall refer to the term of this Agreement, as set forth in
Section 5.1.

         1.38 "TERRITORY" shall mean the United States (including its
territories and possessions and Puerto Rico).

         1.39 "THIRD PARTY" shall mean any party other than a Party, or an
Affiliate of a Party, to this Agreement.

         1.40 "UNIT" shall mean single dose shipping units of any Agent.

2.       SUPPLY; PRICE.

         2.1 SUPPLY FOR CYTOGEN PROJECT; PROMOTIONAL SAMPLES. During the term of
the Marketing Agreement, AM shall supply to Cytogen such completely finished,
vialed, labeled, and finally packaged quantities of Agent as may be reasonably
required by Cytogen and are reasonably acceptable to AM in order to perform the
Cytogen Project or for reasonable distribution of samples to promote sales of
Agent. In addition to sample and commercial presentations of Agent, AM will
provide Agent to Cytogen in such other presentation as Cytogen shall reasonably
request, provided that such other presentations are in compliance with the FDCA
and FDA regulations and that Cytogen pays AM's costs occasioned by developing
the new presentations. Cytogen agrees not to use Agents supplied to it pursuant
to this Section 2.1 for any purpose other than to perform the Cytogen Project or
as promotional samples for which Cytogen receives no consideration. In
consideration of its purchase of any Agent under this Section 2.1, Cytogen shall
pay to AM an amount equal to AM's Cost of Manufacturing such Agent, as AM shall
determine once per year and provide notice thereof to Cytogen. AM's "Cost of
Manufacturing" for purposes of this Section 2.1 shall mean the costs directly
attributable (excluding all overhead) to manufacturing, finishing, packaging and
labeling such Agent (i.e., those costs which vary with production), including,
but not limited to, direct labor and benefit expenses, consumable bulk and other
production materials, determined in accordance with generally accepted cost
accounting practices and

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costs related to outsourcing processes. AM shall invoice Cytogen at the time of
shipment. Payment of such amounts shall be made in accordance with the terms of
subsection 3.7(a). Cytogen shall have the right, upon reasonable prior notice to
AM, at reasonable times and at its own expense to examine or to have examined by
a certified public accountant or other person reasonably acceptable to AM,
pertinent books and records of AM, for the purpose of determining the
correctness of payments made hereunder.

         2.2 SUPPLY. During the term of the Marketing Agreement and for any
extension agreed upon by the Parties, AM agrees to manufacture for and sell
to Cytogen such finished and packaged quantities of Agent as may be
reasonably required by Cytogen for sale in the Territory (except to the
extent that if for any three month period such requirements exceed *****
percent (*****%) of the quantity forecasted for such period by Cytogen, AM
shall only be required to use its commercially reasonable efforts to supply
Cytogen its reasonable requirements of Agent for such sale, but not less than
***** percent (*****%) of the forecast).

         AM agrees that as part of its obligation to manufacture and supply
Cytogen with Agent under this Agreement that such Agent shall be supplied in
completely finished, labeled, and final packaged quantities, containing all
necessary and appropriate packaging and labeling (including, but not limited to,
vials, filters, boxes, inserts, labels, freeze/temperature indicators, as
required by law and agreed to by the Parties), suitable for sale by Cytogen, its
Affiliates or distributors to their respective customers in the Territory and in
accordance with Section 3.9 of this Agreement.

         2.3 PRICE. In consideration of its purchase of Agent (other than
pursuant to Section 2.1), and the rights granted hereunder, Cytogen shall pay to
AM the following Purchase Prices:

             a) $***** per Unit of Feridex I.V.;
             b) $***** per Unit of Combidex; and
             c) $***** per Unit of Code 7228.

         Each Purchase Price shall be payable for so long as AM continues to
provide Agent to Cytogen under this Article and pursuant to Cytogen's orders,
as set forth in Article 3 of this Agreement. Payment of such amounts shall be
made in accordance with subsection 3.7(b). Each Purchase Price is subject to
adjustment at the option of AM beginning on ***** and on each *****
thereafter based upon the ***** from the ***** of such ***** to the *****
of such  ***** of the PPI-06-35 (for Pharmaceutical Preps, ethical) as
published by

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      and Exchange Commission.

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the Bureau of Labor Statistics, US Department of Labor. In the event that
Cytogen's gross margins on the sales of any Agent in any Contract Year
(determined as the quotient of (i) Agent Net Sales for such Agent less the
sum of (x) the aggregate Purchase Price for such Agent invoiced to Cytogen
and (y) royalties owed by Cytogen under the Marketing Agreement for a
Contract Year divided by (ii) Agent Net Sales for such Agent in that Contract
Year) are less than *****%, then at the request of Cytogen, the Parties shall
negotiate in good faith a new Purchase Price with respect to such Agent.

         2.4 ALTERNATE MANUFACTURER. AM shall have the right to contract with
Third Parties to manufacture Agent for supply to Cytogen, provided that AM shall
remain liable to Cytogen for its obligations hereunder and the action or
inaction of any such Third Party.

3.       FORECASTS; ORDERS; MANUFACTURING; DELIVERY; PAYMENT; PACKAGING;
         REPORTS; TAXES.

         3.1 FORECASTS. As soon as practicable following the Effective Date of
this Agreement but no later than the submission of Cytogen's initial purchase
order for any Agent, Cytogen shall send to AM, Cytogen's initial non-binding
forecasts by Contract Quarter of the quantity of each of Combidex, Code 7228 and
Feridex I.V., which Cytogen expects to purchase from AM during the first
Contract Year for each such Agent. At each time purchase orders are submitted by
Cytogen, a revised non-binding forecast by Contract Quarter for each Agent shall
be transmitted by Cytogen to AM for the twelve (12) month period beginning with
the Contract Quarter following the Contract Quarter in which the purchase
order(s) is submitted.

         3.2 ORDERS. Having regard for the forecasts hereinabove referred to,
Cytogen shall furnish AM with purchase order(s) (each, an "Order") at least
three (3) months prior to the beginning of each Contract Quarter commencing
with the second Contract Quarter, consistent with AM's Batch sizes, for the
quantities of each of the Agents which Cytogen shall purchase, and which AM
shall deliver during the upcoming Contract Quarter. Orders for any Agent in a
Contract Quarter in excess of *****% of any of the volume forecasts by
Cytogen for such quarter which AM is not able to fill shall not trigger
Cytogen's alternate supply right under this Agreement or be deemed a breach
of this Agreement. AM agrees to use commercially reasonable efforts to
accommodate purchase order revisions submitted in writing by

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      and Exchange Commission.

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Cytogen. Each Order must specify a delivery date not less than sixty (60) days
after the date of the Order in the case of Combidex and Code 7228 (which period
shall be reduced to thirty (30) days on and after the first anniversary of the
Combidex Approval Date and Code 7228 Approval Date, as the case may be) and in
the case of Feridex, not less than thirty (30) days after the date of the Order.
Unless AM is not able to fill an Order, AM shall acknowledge and accept in
writing each such Order within ten (10) days after receipt of such Order, and
shall confirm the shipment instructions and delivery times for such Order either
to Cytogen or as otherwise directed by Cytogen. If AM is not able to fill an
Order, it shall so notify Cytogen within five (5) days. The purchase order which
will be utilized for such order shall be in such form as may be agreed to by AM
and Cytogen. If there is any conflict between the terms of a purchase order and
the terms of this Agreement, the terms of this Agreement shall govern, unless
the Parties have otherwise expressly agreed in writing. Cytogen's initial Order
for each Agent shall be submitted to AM at least sixty (60) days prior to the
first delivery date specified therein.

         3.3 MANUFACTURING. AM shall manufacture each Agent in accordance with
applicable GMPs, and as described in the applicable NDA (and if applicable DMF)
for each Agent. AM shall manufacture Agent in accordance with the
Specifications. AM shall release any Batch of Agent for delivery to Cytogen
after determining that such Agent meets the Specifications. AM's testing
certificate of analysis ("COA") and a copy of the Batch records shall be shipped
to Cytogen either in advance of or with the Batch of Agent to which each refers.

         3.4 DELIVERY; SHIPMENT. Actual quantities of Agent to be produced and
delivered, and delivery dates, shall be specified in the Orders submitted by
Cytogen; provided each Order quantity shall be in whole Batch Multiples. AM
agrees to ship the quantities of Agent ordered by Cytogen by the common carrier
and method of shipment designated by Cytogen, F.O.B. AM's manufacturing
facility, according to any reasonable shipping schedule specified by Cytogen, to
the locations specified in Cytogen's Orders. Each shipment of Agent shall be
accompanied by an invoice setting forth the amount payable by Cytogen to AM with
respect to such shipment. Cytogen shall pay all costs of shipping.

         3.5 TITLE; LOSS. Legal title and risk of loss with respect to Agent
furnished hereunder by AM shall pass to Cytogen upon delivery to the common
carrier designated by Cytogen at the shipping point at AM's manufacturing
facility.

         3.6 ACCEPTANCE; REJECTION.
                  (a) AM shall deliver Batches of Agent pursuant to Cytogen's
Orders along with a COA. Within twenty (20) days of receipt of any shipment,
Cytogen shall inspect the

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shipment and notify AM of its rejection of any Agent within the Shipment. Agent
may be rejected only if the quantity shipped is inaccurate as compared to the
Order, the shipment does not include the COA or if vials of Agent are damaged or
mislabeled. If Cytogen does not notify AM of rejection within twenty (20) days,
it shall be deemed to have accepted the shipment or any Agent not so rejected.

                  (b) Rejected Agent shall be returned to AM or disposed of at
the direction of AM, in either case at the expense of AM.

                  (c) No rejected Agent shall be reworked by AM unless the same
is expressly permitted in the NDA (or if applicable, DMF).

                  (d) AM shall have seventy-five (75) days after receipt of a
notice from Cytogen rejecting any Batch of Agent to replace the defective Batch.

         3.7 PAYMENTS AND REPORTS FOR AGENTS.
                  (a) Cytogen shall pay for all Agent supplied by AM within
thirty (30) days after receipt of an invoice from AM.

                  (b) Interest on all payments due to AM and not paid by Cytogen
shall accrue at a rate of 12% per annum or the maximum rate allowed by law, if
less.

                  (c) Within thirty (30) days after the close of each Contract
Quarter after Cytogen commences sales of an Agent, Cytogen shall deliver to AM a
report containing an accounting to AM with respect to all Agent Net Sales for
such Contract Quarter and a calculation of gross margin pursuant to Section 2.3.

         3.8 CURRENCY. All payments payable under this Agreement shall be paid
in U.S. dollars in immediately available funds to an account designated by AM.

         3.9 PACKAGING. Agent shall be packaged under Cytogen's label by AM,
with such labeling and packaging inserts as mutually agreed to by the Parties.
Any packaging and labeling changes for any Agent which are required by the FDA
or other regulatory agencies, or changes which result in improved safety or
administration of any Agent, such as those which limit breakage, shall be made
by AM at no additional cost to Cytogen. Any "esthetic" or non-required packaging
and labeling changes requested by Cytogen will be paid for by Cytogen following
agreement by the Parties as to the amounts to be charged to Cytogen by AM.
Notwithstanding any other provision in this Agreement, but subject to Section
3.5 of the Marketing Agreement, Cytogen will submit all proposed advertising for
any Agent directly to the FDA with copies to AM, it being understood that AM
does not expect to comment on advertising by Cytogen or on trivial or aesthetic
changes in packaging, such as type size. Subject to Section 3.5 of the

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Marketing Agreement, if AM does not object to any labeling, packaging or
advertising proposed by Cytogen within five (5) days of communication thereof to
AM by Cytogen in writing, AM shall be deemed to have consented to such labeling,
packaging or advertising.

         3.10 STABILITY, RECORD KEEPING, INSPECTION, ETC. AM will: (i) select
and retain samples of each Batch of Agent as required by the GMPs, and conduct
an ongoing stability program in accordance with the provisions of the GMPs for
finished pharmaceuticals and the NDA (or if applicable, DMF) (or any stability
protocol mutually agreed to by the Parties), and initiate and maintain all
legally required documents and records including, without limitation, Batch and
Lot production, quality control and stability records, for such periods as are
required by the FDA; (ii) promptly notify Cytogen if any out-of-specification
value is found in the stability testing program, and reach agreement with
Cytogen concerning a course of action; (iii) furnish Cytogen with copies of all
such records at Cytogen's request; (iv) if requested by Cytogen, conduct
additional testing of retained samples of any Agent returned by customers to
determine conformity with the Specifications and other requirements of the NDA
(and if applicable DMF); (v) at Cytogen's option and upon reasonable notice to
AM, allow one or more Cytogen quality assurance employees or agents, under
conditions of confidentiality and AM's standard security procedures, to observe
the entire process of manufacture and packaging of each Batch or Lot, or
selected Batches or Lots of Agents; (vi) promptly inform Cytogen of any actual
or threatened legal or regulatory action by the FDA or any other governmental
agency with respect to, or any inspection by the FDA or any other governmental
agency of, the AM facilities or operations relating to the Agents, and provide
Cytogen with any documentation relating thereto or resulting therefrom; (vii)
provide reasonable advance written notice to Cytogen prior to amending the NDA,
or any DMF that is referenced in the NDA; and (viii) store, ship and dispose of
all wastes generated as a result of its manufacture of Agent in accordance with
all applicable laws and regulations.

         3.11     RECALL PROCEDURE, COMPLAINTS, ADVERSE EVENT REPORTING, ETC.

                  (a) If Cytogen learns of any information that might give rise
to a recall or market withdrawal of any Agent or which might result in a field
alert report pursuant to the NDA, or which involves a complaint about the
quality or purity of any Agent, then Cytogen shall promptly provide notice
thereof to AM. With respect to any Agent, and as between Cytogen and AM,
initiation of any recall or market withdrawal, any investigation of any product
complaint, or the filing of any field alert report with the FDA, shall be the
responsibility of AM, and AM shall be responsible for and handling of all

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interaction with the FDA and other governmental authorities. To the extent
possible under the circumstances, AM will inform Cytogen prior to communicating
with the FDA concerning any recall, market withdrawal or field alert report
involving any Agent distributed by Cytogen.

                  (b) If in any case where Cytogen's name is on the label of an
Agent and Cytogen is of the opinion that a report to a regulatory agency must be
made, or a recall or market withdrawal initiated, and such action has not been
taken diligently by AM, then Cytogen shall have the right to take such action,
if required by law, except that Cytogen will not initiate a recall or market
withdrawal without first discussing the matter with the FDA.

                  (c) Any U.S. adverse event report or medical complaint
received by Cytogen or AM relating to an Agent shall be promptly investigated by
Cytogen. Cytogen will notify AM within one working day of becoming aware of an
adverse event or medical complaint. AM will notify Cytogen within one working
day of becoming aware of an adverse event or medical complaint, providing
appropriate contact information to allow for Cytogen follow-up. Adverse events
from outside the U.S. will be followed up by AM. Copies of serious (FDA defined)
non-U.S. cases will be transmitted to Cytogen within five (5) working days of AM
becoming aware of the case. Any such report that involves an event that is both
serious and unexpected (as those terms are defined by then applicable FDA
regulations) will be promptly reported to the FDA by Cytogen within fifteen (15)
working days of receipt (term definition and reporting requirements to be
modified to meet then applicable regulations). Cytogen will provide AM with
copies of completed serious (FDA defined) U.S. cases within five (5) working
days of Cytogen becoming aware of the case. Cytogen will prepare adverse event
periodic reports in accordance with FDA regulations. Periodic reports will be
forwarded to AM within twenty-five (25) days of close of the reporting interval,
AM will be responsible for submission of periodic and other non-fifteen (15) day
reports to the FDA. Each respective Party will provide the other Party with
monthly updates of adverse event and product complaint activity within ten (10)
days of the end of each month.

         3.12 CONTINUING GUARANTEE. For the purpose of Section 333(c)(2) of the
FDCA, AM and Cytogen each hereby guarantee to the other that, as of the date of
each shipment by AM to Cytogen (in the case of AM's guarantee) and by Cytogen to
purchasers from it (in the case of Cytogen's guarantee) of any Agent subject to
the provisions of the FDCA, such Agent is not, when shipped by it, adulterated
or misbranded within the meaning of the FDCA or of any applicable state law in
which the definitions of adulteration and misbranding are substantially the same
as those contained in the FDCA. AM and

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Cytogen each hereby guarantee to the other that, as of the date of each such
shipment by it, such Agent will not be an article which may not, under the
provisions of Sections 344 or 355 of the FDCA, be introduced into interstate
commerce.

         3.13 TAXES. Cytogen shall pay all taxes on the use or sale of Agent
supplied to Cytogen other than AM's income taxes which may result in connection
with this Agreement.

4.       LICENSE TO MANUFACTURE AGENT.

         4.1 LICENSE TO MANUFACTURE AGENT. If (i) at any time during the term
of this Agreement, AM (A) notifies Cytogen that it will be unable to provide
at least *****% of the quantity of Agent projected to be needed in any of
Cytogen's forecasts; or (B) fails for any reason, including by reason of an
event specified in Section 9.1 hereof, to supply Cytogen with any Agent in
accordance with Orders submitted by Cytogen and such failure continues for
ninety (90) days in the case of Code 7228 and Combidex (which period shall be
increased to one hundred and twenty (120) days on and after the first
anniversary of the Code 7228 Approval Date or Combidex Approval Date, as the
case may be), or one hundred and twenty (120) days in the case of Feridex
I.V., or (ii) AM fails to supply Cytogen with Combidex after the Combidex
Approval Letter Date or Code 7228 after the Code 7228 Approval Letter Date,
in accordance with the initial Order submitted by Cytogen hereunder to
purchase such Agent from AM for commercial resale in the United States, and
such failure continues for ninety (90) days after the respective Approval
Letter Date, AM shall grant Cytogen a temporary non-exclusive right and
license, to manufacture the particular Agent to which such failure relates,
and AM shall, subject to the provisions of Section 4.3 hereof, provide to
Cytogen all Manufacturing Technology necessary to enable Cytogen to
manufacture such Agent. The temporary right and license which may be granted
pursuant to this Section 4.1 shall include a right to sublicense to an
Affiliate or a Third Party contract manufacturer reasonably satisfactory to
AM, subject to the confidentiality provisions of Article 7; PROVIDED, that
Cytogen shall be liable for the compliance by such Affiliate or Third Party
contract manufacturer reasonably satisfactory to AM with all applicable terms
of this Agreement.

         If Cytogen is granted such license to manufacture, it shall have the
right, but not the obligation, to manufacture such Agent; and the failure of
Cytogen to manufacture, or have manufactured, such Agent shall not cause Cytogen
to be in breach of any obligation it may have under this Agreement absent bad
faith or willful misconduct.

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      and Exchange Commission.

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         If a condition specified in clause (i) of this Section occurs and is
continuing for a period of six months (including the 90-day or 120-day period,
as applicable, referred to in clause (i)) or the condition specified in clause
(ii) of this Section occurs and is continuing for a period of ninety (90) days,
then AM and Cytogen shall negotiate in good faith with a view to (x) modifying
the percentage amount of the royalty under Section 10.1 of the Marketing
Agreement in light of the costs to Cytogen of AM's failure to supply (or cause a
Third Party or Affiliate to supply) Cytogen with such Agent, (y) establishing a
date by which AM shall resume manufacturing such Agent, and (z) affording
Cytogen the right to terminate this Agreement if AM shall not resume
manufacturing by such date, and, if AM and Cytogen are not able to agree on a
modified royalty percentage and date for resumption by AM of manufacturing such
Agent, then Cytogen shall be entitled to terminate this Agreement pursuant to
Section 5.1(c). The temporary license and right of termination set forth in this
Section shall be Cytogen's only remedy for AM's failure to manufacture or
deliver any Agent, absent bad faith or willful misconduct by AM.

         4.2 LICENSE DURATION. The temporary right and license which may be
granted pursuant to this Section shall continue until AM notifies Cytogen that
it is capable and willing to resume the supply and delivery to Cytogen of its
requirements of such Agent (the "Notification"). Upon the expiration of any
temporary right and license which may be granted pursuant to this Article 4,
Cytogen and the manufacturer used by Cytogen shall return the Manufacturing
Technology to AM or otherwise dispose of such Manufacturing Technology as
instructed by AM and AM shall resume supplying such Agent pursuant to Article 3.
The obligation of Cytogen to make the royalty payments pursuant to Section 10.1
of the Marketing Agreement shall continue notwithstanding any grant to Cytogen
of the right and license to manufacture any Agent set forth in this Article 4.

         4.3 DISCLOSURE OF MANUFACTURING TECHNOLOGY TO CYTOGEN. If AM grants a
license to Cytogen to manufacture an Agent pursuant to this Article, AM shall,
at Cytogen's reasonable request, disclose and deliver to such Qualified Persons
as shall be designated by Cytogen to AM any or all of the Manufacturing
Technology and Agent Technology, including documents, drawings, specifications,
processes, formulations, protocols, devices and other tangible manifestations
thereof, necessary to enable Cytogen to Qualify itself, its Affiliates or a
Third Party, as the case may be, and to exercise its rights under said license
with respect to the particular Agent for which the license is being granted.
Cytogen shall not disclose any Agent Technology or Manufacturing Technology
disclosed to it pursuant to this Section to any other Person, whether or not
such Person is an Affiliate of Cytogen, without the express

                                      -13-
<PAGE>

permission of AM, except as expressly permitted in Article 6 of the Marketing
Agreement regarding Agent Technology, nor may Cytogen use any of such Agent
Technology or Manufacturing Technology except as expressly permitted by this
Agreement or the Marketing Agreement.

         4.4 INSPECTION RIGHT. If Cytogen shall manufacture, or have
manufactured, any Agent pursuant to Section 4.1, AM shall have the right with
prior written notice of no less than ten (10) days, during normal business
hours, to inspect the finished Agent upon and in connection with which any
Trademark is to be used, as well as the methods of manufacture used by Cytogen
(or any Affiliate or Third Party engaged in manufacture of such Agent pursuant
to Section 4.1) in order that AM may satisfy itself that the finished Agent
meets its formulae, standards, specifications and instructions. If any finished
Agent is unsatisfactory in the reasonable opinion of AM, Cytogen and AM shall
meet to discuss AM's opinion of why such Agent is unsatisfactory.

5.       TERM; TERMINATION; SURVIVAL.

         5.1 TERM. This Agreement shall continue in force until August ___,
2010, with rolling automatic successive renewal periods of additional five (5)
years, unless notice of non-renewal or termination is given by Cytogen or AM
ninety (90) days prior to the commencement of any renewal period, and unless and
until terminated pursuant to the provisions of this Section. This Agreement
shall be automatically terminated upon termination of the Marketing Agreement.
In addition, this Agreement may be terminated:

                  (a) at any time, by Cytogen or AM if the other Party shall
materially breach any of the terms, conditions and agreements contained herein
to be kept, observed, and performed by it, in which case the non-breaching Party
may terminate this Agreement at its option and without prejudice to any of its
other legal and equitable rights or remedies except as specifically provided in
this Agreement, by giving the Party which committed the breach sixty (60) days
written notice, particularly specifying the breach, unless the notified Party
within such sixty (60) days shall have cured the breach;

                  (b) at any time, if any assignment shall be made by either
Party for the benefit of creditors, or if a receiver, trustee in bankruptcy or
similar officer shall be appointed to take charge of all of the property of
either Party, or if either Party files a voluntary petition under applicable
bankruptcy laws or such a petition is filed against either Party and is not
dismissed within sixty (60) days, the other Party may immediately terminate this
Agreement by giving written notice of termination;

                                      -14-
<PAGE>

                  (c) by Cytogen, upon thirty (30) days notice, upon the
occurrence of any condition specified in clause (i) of Section 4.1, which
condition continues for a period of six (6) months, or (ii) upon the occurrence
of a condition specified in clause (ii) of Section 4.1, which condition
continues for a period of ninety (90) days, during which AM is not able to cause
any other Third Party reasonably acceptable to Cytogen to commence performing
AM's manufacturing obligations pursuant to this Agreement, and AM and Cytogen
are not able to agree upon a revised royalty percentage and date by which AM
shall resume manufacturing that particular Agent.

         5.2 EFFECT OF TERMINATION.
                  (a) Expiration or termination of this Agreement shall result
in the termination of all provisions hereof unless otherwise specified,
including, without limitation, the payment and the supply obligation herein
contained; PROVIDED that Cytogen shall continue to be liable for payments
(with respect to all Agent that have then been delivered to or at the direction
of Cytogen) that shall then have accrued and provided that sections 1, 5.2, 6,
7 and 9 shall survive any expiration or termination.

                  (b) Upon expiration or termination of this Agreement: (i)
Cytogen shall immediately return to AM the Manufacturing Technology and Agent
Technology, if any, in its possession, or otherwise dispose of such
Manufacturing Technology and Agent Technology as instructed by AM and cause any
Affiliates or Approved Sublicenses to do the same; and (ii) each Party shall
immediately return any confidential information of the other.

                  (c) Upon termination of this Agreement by AM, Cytogen shall
have the right to complete the sale of its inventory of Agent in the Territory;
PROVIDED, that Cytogen's obligations hereunder to comply with the provisions of
Articles 2 and 3 in connection with such completion of sale shall remain in
effect; and PROVIDED FURTHER, that if requested by AM, Cytogen shall negotiate
with AM for the sale of Cytogen's entire inventory of Agent to AM on terms to be
negotiated by the parties at such time.

                  (d) Upon expiration or termination of this Agreement, neither
Party shall have liability to the other Party for damages of any kind solely as
a result of the fact of such expiration or termination, whether on account of
the loss by Cytogen of present or prospective sales, investments or goodwill
arising solely from statutes that relate to termination of distributors or
licensees, and each Party hereby waives any rights which may be granted to it by
such statutes. The termination of this Agreement by either party pursuant to
this Section shall not bar the party terminating the Agreement from pursuing

                                      -15-
<PAGE>

other legal remedies against the other party including, without limitation,
monetary damages for breach of contract.

6.       DISCLAIMERS; INDEMNITY.

         6.1      (a) AM makes the following warranties with
respect to Agent manufactured by AM and delivered to Cytogen by AM under this
Agreement: (i) the Agent shall be manufactured in accordance with the
approved NDA covering such Agent and the requirements of the FDA and shall
conform to the specifications set forth in the approved NDA at the time of
delivery, (ii) AM shall comply with all other statutes and regulations
applicable to the manufacturing of such Agent at the time of production
(including without limitation, those relating to the generation, storage,
shipment and disposal of waste); and (iii) AM has not used in any capacity
under this Agreement or the Marketing Agreement any person who has been
debarred pursuant to the FDCA.

                  (b) EXCEPT AS SPECIFICALLY SET FORTH IN THIS AGREEMENT AND
PARAGRAPHS (c) AND (d) BELOW, AND TO THE MAXIMUM EXTENT PERMITTED BY LAW, AM
DISCLAIMS ANY EXPRESS OR IMPLIED WARRANTY (I) THAT THE AGENT TECHNOLOGY OR THE
MANUFACTURING TECHNOLOGY, OR THE USE THEREOF, OR ANY PRODUCTS INCORPORATED OR
MANUFACTURED BY THE USE THEREOF, WILL BE FREE FROM CLAIMS OF PATENT
INFRINGEMENT, INTERFERENCE OR UNLAWFUL USE OF PROPRIETARY INFORMATION OF ANY
THIRD PARTY AND (II) OF THE ACCURACY, RELIABILITY, TECHNOLOGICAL OR COMMERCIAL
VALUE, COMPREHENSIVENESS, OR MERCHANTABILITY OF THE AGENT TECHNOLOGY OR THE
MANUFACTURING TECHNOLOGY, OR ANY AGENT OR ANY OTHER PRODUCTS INCORPORATED OR
MANUFACTURED BY THE USE THEREOF, OR THEIR SUITABILITY OR FITNESS FOR ANY PURPOSE
WHATSOEVER INCLUDING, WITHOUT LIMITATION, THE DESIGN, DEVELOPMENT, MANUFACTURE,
USE OR SALE OF ANY AGENT. AM DISCLAIMS ALL OTHER WARRANTIES OF WHATEVER NATURE,
EXPRESS OR IMPLIED. EXCEPT AS PROVIDED IN PARAGRAPH (c) BELOW, AM'S LIABILITY
ARISING OUT OF THE FAILURE OF ANY AGENT MANUFACTURED BY OR FOR IT TO CONFORM TO
THE WARRANTY SET FORTH IN SECTION 6.1(a) WHETHER BASED UPON WARRANTY, CONTRACT,
TORT (INCLUDING WITHOUT LIMITATION, NEGLIGENCE) OR OTHERWISE, SHALL BE LIMITED
TO REPLACEMENT OF THE DEFECTIVE AGENT IN THE ABSENCE OF AM'S BAD FAITH OR

                                      -16-
<PAGE>

WILLFUL MISCONDUCT. AM'S LIABILITY FOR FAILURE TO MANUFACTURE OR SUPPLY ANY
AGENT PURSUANT TO CYTOGEN'S ORDERS SHALL BE LIMITED TO THE RIGHTS SPECIFIED IN
ARTICLE 4 OF THIS AGREEMENT IN THE ABSENCE OF AM'S BAD FAITH OR WILLFUL
MISCONDUCT. AM'S LIABILITY IF IT IS ALLEGED OR DETERMINED THAT CYTOGEN'S
EXERCISE OF ANY OF ITS RIGHTS HEREUNDER WOULD INFRINGE UPON, OR CONFLICT WITH,
ANY PATENT OR OTHER PROPRIETARY RIGHT OF ANY THIRD PARTY SHALL BE LIMITED TO THE
RIGHTS SET FORTH IN SECTION 8.2 OF THE MARKETING AGREEMENT.

                  (c) AM will indemnify and hold harmless Cytogen, each
Affiliate of Cytogen and their respective officers, directors, and employees
against any out-of-pocket costs resulting from any claim of product liability,
including due to any bodily injury or death, or product recall or FDA
investigation costs (for purposes of this Section, any out-of-pocket cost
resulting from a claim of product liability, or product recall or FDA
investigation cost hereinafter referred to as a "Claim") that may be incurred by
Cytogen or any such Affiliate, officer, director or employee to the extent such
Claim arises or is alleged to arise out of a material breach by AM of the AM
warranty set forth in the Section 6.1(a) above.

                  (d) Cytogen will indemnify and hold harmless AM, each
Affiliate of AM, and their respective officers, directors and employees against
any out-of-pocket Claim that may be incurred by AM or any such Affiliate,
officer, director, or employee to the extent such out-of-pocket Claim arises or
is alleged to arise out of the use or sale by Cytogen, its Affiliates or
Approved Sublicensees of any Agent manufactured by AM, Cytogen, any Affiliate of
Cytogen, or Cytogen designee, provided, however that Cytogen does not indemnify
and hold harmless AM, each Affiliate of AM and their respective officers,
directors and employees from any out-of-pocket Claim to the extent such
out-of-pocket Claim arises out of a breach by AM of the warranty set forth in
Section 6.1(a) above.

                  (e)      (i) Each indemnified party agrees to give the
indemnifying party prompt written notice of any Claim or discovery of fact upon
which such indemnified party intends to base a request for indemnification
hereunder.

                           (ii)  Each party shall furnish promptly to the
other copies of all papers and official documents received in respect of any
claim for indemnification. The indemnified party will cooperate with the
indemnifying party in providing witnesses and records necessary in the
defense against any such claim.

                                      -17-
<PAGE>

                           (iii) With respect to any Claim relating solely to
the payment of money damages and which will not result in the indemnified
party's becoming subject to injunctive or other relief or otherwise adversely
affect the business of the indemnified party in any manner as to which the
indemnifying party shall have acknowledged in writing the obligation to
indemnify the indemnified party hereunder, the indemnifying party shall have the
sole right to defend, settle or otherwise dispose of such claim, on such terms
as the indemnifying party, in its sole discretion shall deem appropriate.

                           (iv) The indemnifying party shall obtain the written
consent of the indemnified party, which shall not be unreasonably withheld,
prior to ceasing to defend, settling or otherwise disposing of any claim if as a
result thereof the indemnified party would become subject to injunctive or other
equitable relief or the business of the indemnified party would be adversely
materially affected. The indemnifying party shall not be liable for any
settlement or other disposition of a Claim by the indemnified party which is
reached without the written consent of the indemnifying party.

                           (v) Except as provided above, the costs and expenses
including fees and disbursements of counsel, incurred by any indemnified party
in connection with any claim shall be reimbursed on a quarterly basis by the
indemnifying party, without prejudice to the indemnifying party's right to
contest the indemnified party's right to indemnification and subject to a refund
in the event that the indemnifying party is ultimately held not to be obligated
to indemnify the indemnified party.

                  (f) EXCEPT IN CONNECTION WITH BREACHES OF THE CONFIDENTIALITY
OBLIGATIONS OF ARTICLE 7 HEREOF OR IN CONNECTION WITH AN INFRINGEMENT OR
MISAPPROPRIATION BY ONE PARTY OF THE INTELLECTUAL PROPERTY OF THE OTHER, IN NO
EVENT SHALL AM OR CYTOGEN BE RESPONSIBLE TO THE OTHER FOR INCIDENTAL OR
CONSEQUENTIAL DAMAGES (INCLUDING, WITHOUT LIMITATION, LOST PROFITS) OF THE OTHER
PARTY.

                  (g) Each Party agrees to obtain and maintain in effect a
policy or policies of insurance covering its indemnity obligations hereunder.
Such policies shall be issued by one or more reputable insurers reasonably
acceptable to the other Party, and shall contain terms of coverage reasonably
acceptable to the other Party. The policy limits of the policy or policies
obtained by Cytogen shall be at least ten million dollars ($10,000,000). The
policy limits of the policy or policies initially obtained by AM shall be at
least five million ($5,000,000), but AM shall use commercially reasonable

                                      -18-
<PAGE>

efforts to increase such coverage to total policy limits of at least ten million
dollars ($10,000,000) by the later of the Combidex Approval Letter Date or the
Code 7228 Approval Letter Date. Upon the request of the other Party to this
Agreement, each Party shall provide evidence of insurance coverage in compliance
with this Section to the other party. In lieu of the insurance coverage
described above, either party shall have the right to undertake a program of
self-insurance to cover its indemnity obligations hereunder; PROVIDED, HOWEVER,
that such program of self-insurance shall be proposed in writing to and approved
by the other party to this Agreement (such approval not to be unreasonably
withheld). The obligations described in this Section shall survive the
termination of this Agreement and continue to bind the parties for five (5)
years after the expiration date of the last unit of Agent distributed by Cytogen
pursuant to this Agreement.

                  (h) Except in connection with a breach of Article 7,
infringement or misappropriation of any intellectual property of the other Party
or liability under Sections 6.1(c) or (d), the maximum liability under this
Agreement shall equal the amount paid by Cytogen under the Cytogen Agreements
over the twelve month period immediately preceding the event giving rise to such
liability.

7.       CONFIDENTIALITY.

         7.1 CONFIDENTIALITY. Except as expressly permitted in this Section 7.1,
Cytogen shall maintain the confidentiality of all Agent Technology and
Manufacturing Technology (collectively "AM Confidential Material"), and not
disclose any such AM Confidential Material to any Person (including its own
employees and agents), other than Qualified Persons who have signed Cytogen's
standard agreement protecting the confidentiality of third party information
prior to such disclosure, and shall hold the same in confidence and shall use
the same only for the purposes specified herein. Notwithstanding anything in
this Agreement to the contrary, Cytogen may disclose such AM Confidential
Information to Affiliates or Approved Sublicensees on a confidential basis to
the extent necessary to enable them to manufacture (to the extent permitted
under Article 4 of this Agreement) Agent; PROVIDED, HOWEVER, that Cytogen shall
be responsible for any failure by any such Affiliate or Approved Sublicensee to
(i) maintain the confidentiality of such information (except as provided in
Section 7.2), (ii) use it only for such purposes and (iii) disclose it only to
employees who need to know such information for such purposes and who have
previously signed Cytogen's standard agreement, referred to above, or are
otherwise bound by obligations substantially similar to those in such standard
agreement, prior to such disclosure.

                                      -19-
<PAGE>

         7.2. EXCEPTIONS.
                  (a) The obligations of confidentiality and restrictions on
use imposed upon Cytogen by Section 7.1 shall not apply to any AM Confidential
Information that was: (i) in the public domain before the date of this
Agreement or subsequently came into the public domain other than through any
disclosure or delivery thereof by Cytogen; or (ii) lawfully received by Cytogen
without an obligation of confidentiality from a source other than AM; or (iii)
disclosed with the prior written approval of AM.

                  (b) Notwithstanding anything to the contrary contained in this
Agreement, Cytogen and its Affiliates and any such Third Party manufacturer may
disclose or deliver any such AM Confidential Information to (i) any government
agency or official to the extent that such disclosure or delivery is necessary
for compliance with any law or regulation or (ii) to any Third Party if required
to be disclosed by governmental or judicial order, in which case Cytogen shall
promptly notify AM and take reasonable steps to assist in contesting such order
or in protecting AM's rights prior to disclosure.

         7.3 SURVIVAL. This Article 7 shall survive termination of this
Agreement for any reason for a period of five (5) years.

8.       COMPLIANCE WITH REGULATIONS. Each Party will comply with, and cause
any of their Affiliates performing any of their respective rights or obligations
hereunder to comply with, all laws and regulations applicable to such rights and
obligations.

9.       MISCELLANEOUS.

         9.1 FORCE MAJEURE. If either Party is prevented from performing, or is
unable to perform, any of its obligations under this Agreement, due to any act
of God, fire, casualty, flood, war, strike, lock out, failure of public
utilities, injunction or any act, exercise, assertion or requirement of
governmental authority, compliance with any law or government regulation or
order, epidemic, destruction of production facilities, insurrection, inability
to procure materials, labor, equipment, transportation or energy sufficient to
meet its production or performance needs, or any other cause beyond the
reasonable control of the Party invoking this provision, and if such Party shall
have used its commercially reasonable efforts to avoid such occurrence and
minimize its duration and has given prompt written notice to the other Party,
then the affected Party's performance shall be excused and the time for
performance shall be extended for the period of delay or ability to perform due
to such occurrence.

         9.2 NOTICES. All notices and other communications under this Agreement
shall be in writing and shall be delivered by hand or overnight courier service,
mailed or sent by telecopier, as follows:

                                      -20-
<PAGE>

                  All notices to AM other than routine correspondence relating
to purchase orders, forecasts, and revisions shall be addressed to:

                  Attention:        Jerome Goldstein
                                    Advanced Magnetics, Inc.
                                    61 Mooney Street
                                    Cambridge, MA  02138
                                    Telecopier: (617) 547-2445

         With a copy addressed to:

                  Attention:        Leslie E. Davis, Esq.
                                    Testa, Hurwitz & Thibeault, LLP
                                    125 High Street
                                    Boston, MA 02110
                                    Telecopier: (617) 248-7100

         Purchase orders, forecasts, revisions, and routine correspondence
relating thereto shall be addressed to:

                  Attention:        Vice President, Operations
                                    Advanced Magnetics, Inc.
                                    61 Mooney Street
                                    Cambridge, MA  02138
                                    Telecopier: (617) 547-2445

         All notices to Cytogen other than routine correspondence relating to
purchase orders, forecasts, and revisions shall be addressed to:

                  Attention:        Dr. Joseph Reiser
                                    Cytogen Corporation
                                    600 College Road East
                                    Princeton, NJ  08540-5308

         With a copy addressed to:

                  Attention:        General Counsel
                                    Cytogen Corporation
                                    600 College Road East, CN5308
                                    Princeton, NJ 08540-5308

                                      -21-
<PAGE>

         Routine correspondence relating to purchase orders, forecasts, and
revisions shall be addressed to:

                  Attention:        Vice President, Sales & Marketing
                                    Cytogen Corporation
                                    600 College Road East, CN5308
                                    Princeton, NJ 08540-5308

or to such other address as any Party may have furnished to the other in writing
in accordance herewith, except that notices of change of address shall only be
effective upon receipt. All notices and other communications given to any Party
hereto in accordance with the provisions of this Agreement shall be deemed to
have been given on the date of receipt if delivered by hand or overnight courier
service or sent by telecopier, or on the date five business days after dispatch
by certified or registered mail if mailed, in each case delivered, sent or
mailed (properly addressed) to such Party as provided in this Section 9.2.

         9.3 ASSIGNMENT. Neither this Agreement nor any rights granted hereby
may be assigned by Cytogen voluntarily or by operation of law, without AM's
prior written consent, which may be granted or withheld in AM's sole discretion.
Assignment shall be deemed to include the transfer of substantially all of the
assets of, or a majority interest in the voting stock of Cytogen, or the merger
of Cytogen with one or more other Persons (except a merger in which the
stockholders of Cytogen prior to the merger constitute the holders of a majority
of the capital stock of the surviving entity following the merger). This
Agreement shall be freely assignable by AM. This Agreement shall be binding
upon, and inure to the benefit of the successors and assigns of AM and the
permitted successors and assigns of Cytogen.

         9.4 GOVERNING LAW. This Agreement shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts, without regard to
conflict of law principles thereof. Each Party irrevocably submits to the
exclusive jurisdiction of any state or federal district court of competent
jurisdiction in the Commonwealth of Massachusetts for the purpose of any suit,
action or other proceeding arising out of this Agreement or any transaction
contemplated by this Agreement (and agrees not to commence any action, suit or
proceeding relating to this Agreement or any such transaction, except

                                      -22-
<PAGE>

in those courts). Each party further agrees that service of any process,
summons, notice or document in accordance with Section 9.3 shall be effective
service of process for any action, suit or proceeding with respect to any
matters to which it has submitted to jurisdiction as set forth in the
immediately preceding sentence. Each party irrevocably and unconditionally
waives any objection to the laying of venue of any action, suit or proceeding
arising out of this Agreement or the transactions contemplated by this Agreement
in any state or federal court of competent jurisdiction in the Commonwealth of
Massachusetts, and further irrevocably and unconditionally waives and agrees not
to plead or claim in any such action, suit or proceeding sought in any such
court that such action, suit or proceeding has been brought in an inconvenient
forum.

         9.5 ENTIRE AGREEMENT. This Agreement constitutes the entire agreement
between the Parties relating to the subject matter hereof. There are no
understandings, agreements, representations or warranties, express or implied,
not specified herein regarding this Agreement or the subject matter hereof.

         9.6 INDEPENDENT CONTRACTORS. No agency, partnership or joint venture is
hereby established. Neither Party shall be responsible for the acts or omissions
of the other Party. Neither Cytogen nor AM shall enter into, or incur, or hold
itself out to Third Parties as having authority to enter into or incur on behalf
of the other Party any contractual obligations, expenses or liabilities
whatsoever.

         9.7 COUNTERPARTS. This Agreement may be executed simultaneously in
several counterparts, each of which shall be deemed an original, but all of
which together shall constitute one and the same instrument.

         9.8 SEVERABILITY. The provisions of this Agreement are severable, and
in the event that any provisions of this Agreement shall be determined to be
invalid or unenforceable under any controlling body of the law, such invalidity
or unenforceability shall not in any way affect the validity or enforceability
of the remaining provisions hereof.

         9.9 HEADINGS. Section and paragraph headings contained in this
Agreement are included for convenience only and form no part of the agreement
between the parties.

         9.10 PUBLICITY. Except as required by or advisable under law,
governmental regulation, judicial order, generally accepted accounting
principals or any obligations pursuant to any listing agreement with, or
regulation of, any national securities exchange or quotation system, neither
Party shall directly or indirectly make any public announcement or publicity
concerning this Agreement or the subject matter hereof without the prior written
consent of the other Party and agreement upon the nature,

                                      -23-
<PAGE>

text and timing of such announcement, which approval and agreement shall not be
unreasonably withheld. Such approval and agreement shall be deemed to be given
if no response is given to the other Party within two working days of receipt of
the proposed text from the Party intending to make such announcement. In the
event of a public announcement or publicity not required by law, the Party
making such announcement shall use its commercially reasonable efforts to
provide the other with a copy of the proposed text prior to such announcement,
for the purpose of notice and opportunity to comment.

         9.11 WAIVER. The waiver by either Party of a breach or a default of any
provision of this Agreement by the other Party shall not be construed as a
waiver of any succeeding breach of the same or any other provisions, nor shall
any delay or omission on the part of either Party to exercise or avail itself of
any right, power or privilege that it has, or may have hereunder, operate as a
waiver of any right, power or privilege by such Party. No waiver, consent,
modification or change of terms of this Agreement shall bind either Party unless
in a writing signed by both Parties, and then such waiver, consent, modification
or change shall be effective only in the specific instance and for the specific
purpose given.

         9.12 SUPERIORITY OF AGREEMENT. The parties agree that the provisions of
this Agreement, together with any amendments hereto and thereto shall prevail
over any inconsistent statements or provisions contained in any documents
passing between the parties, including, but not limited to, any purchase order,
acknowledgment, confirmation, or notice.

                  [REMAINDER OF PAGE LEFT INTENTIONALLY BLANK]

                                      -24-
<PAGE>

                  IN WITNESS WHEREOF, this Agreement has been duly executed as a
sealed instrument as of the date specified above.

CYTOGEN CORPORATION                                 ADVANCED MAGNETICS, INC.

By: /s/ H. Joseph Reiser                            By: /s/ Jerome Goldstein
   -------------------------------------               ------------------------
   President and Chief Executive Officer               Jerome Goldstein
                                                       Chief Executive Officer

                                      -25-
<PAGE>

                                                                      EXHIBIT A

                                 SPECIFICATIONS

                   REGULATORY SPECIFICATIONS FOR FERIDEX I.V.

<TABLE>
<S>                                                          <C>
----------------------------------------------------------------------------------------------------------------------
TEST                                                         Proposed Regulatory Specifications
----------------------------------------------------------------------------------------------------------------------
APPEARANCE                                                   Black to reddish brown liquid
----------------------------------------------------------------------------------------------------------------------
PHYSICAL TEST

----------------------------------------------------------------------------------------------------------------------
         pH                                                  5.0-9.0
----------------------------------------------------------------------------------------------------------------------
         Relaxivity                                          0.55-1.25 x 10(5)  M(-1) sec(-1)
----------------------------------------------------------------------------------------------------------------------
         Magnetic Susceptibility                             Not less than 17,000 x 10(-6) c.g.s units/g of iron
----------------------------------------------------------------------------------------------------------------------
                  Colloidal Particle Size                    100-250 nm Effective Diameter
----------------------------------------------------------------------------------------------------------------------
                  Osmolality                                 325-365 mOsm/kg
----------------------------------------------------------------------------------------------------------------------
                  Specific Gravity                           1.031-1.041
----------------------------------------------------------------------------------------------------------------------
                  Identification                             No precipitate with ammonium hydroxide; brown
                                                             precipitate with hydrochloric acid followed by ammonium
                                                             hydroxide
----------------------------------------------------------------------------------------------------------------------
MICROBIOLOGICAL TEST
----------------------------------------------------------------------------------------------------------------------

</TABLE>

<PAGE>

<TABLE>
<CAPTION>
<S>                                                          <C>
----------------------------------------------------------------------------------------------------------------------
                  Sterility                                  Pass
----------------------------------------------------------------------------------------------------------------------
                  Bacterial Exdotoxin                        Less than 12.5 EU/ml
----------------------------------------------------------------------------------------------------------------------
CONTENT TESTS
----------------------------------------------------------------------------------------------------------------------
                  Iron Content                               10.7-11.7 mg/ml
----------------------------------------------------------------------------------------------------------------------
                  Dextran Content                            5.6-9.1 mg/ml
----------------------------------------------------------------------------------------------------------------------
                  Mannitol Content                           55.2-67.4 mg/ml
----------------------------------------------------------------------------------------------------------------------
                  Citrate Content                            0.25-0.53 mg/ml
----------------------------------------------------------------------------------------------------------------------
                  Volume per Vial                            5.0-5.6 ml
----------------------------------------------------------------------------------------------------------------------
                  Free Iron                                  Less than 0.10 mg/ml
----------------------------------------------------------------------------------------------------------------------
</TABLE>

<PAGE>

                     REGULATORY SPECIFICATIONS FOR COMBIDEX

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------
CODE 7227 TESTING                          *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
<S>                                        <C>                                         <C>
PHYSICAL TEST
------------------------------------------------------------------------------------------------------------------------------
Appearance                                 *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Identification                             *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
pH                                         *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Susceptibility                             *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Size                                       *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
MICROBIOLOGICAL TESTS
------------------------------------------------------------------------------------------------------------------------------
Bacterial endotoxin                        *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Sterility*                                 *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Content Tests
------------------------------------------------------------------------------------------------------------------------------
Iron content                               *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Dextran content                            *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Sodium citrate content                     *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Moisture content                           *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Colloidal iron                             *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
Ionic iron                                 *****                                       *****
------------------------------------------------------------------------------------------------------------------------------
</TABLE>

----------------------------------
***** Confidential portion omitted and filed separately with the Securities
      and Exchange Commission.

<PAGE>

                     REGULATORY SPECIFICATIONS FOR CODE 7228
<TABLE>
<CAPTION>
------------------------------------------------------------------------------------------------------------------------------
TEST                                                         *****
------------------------------------------------------------------------------------------------------------------------------
<S>                                                          <C>
PHYSICAL TESTS
------------------------------------------------------------------------------------------------------------------------------
Appearance                                                   *****
------------------------------------------------------------------------------------------------------------------------------
Identification (FTIR)                                        *****
------------------------------------------------------------------------------------------------------------------------------
pH                                                           *****
------------------------------------------------------------------------------------------------------------------------------
Magnetic Susceptibility                                      *****
------------------------------------------------------------------------------------------------------------------------------
Particle Size                                                *****
------------------------------------------------------------------------------------------------------------------------------
Vol./Vial ml                                                 *****
------------------------------------------------------------------------------------------------------------------------------
Osmolality                                                   *****
------------------------------------------------------------------------------------------------------------------------------
Biological Test
------------------------------------------------------------------------------------------------------------------------------
Sterility                                                    *****
------------------------------------------------------------------------------------------------------------------------------
Bacterial Endotoxin                                          *****
------------------------------------------------------------------------------------------------------------------------------
Content Tests
------------------------------------------------------------------------------------------------------------------------------
Total Organic Carbon (TOC) (mg/g)                            *****
------------------------------------------------------------------------------------------------------------------------------
Iron Content                                                 *****
------------------------------------------------------------------------------------------------------------------------------
Ionic Iron                                                   *****
------------------------------------------------------------------------------------------------------------------------------
Colloidal Iron                                               *****
------------------------------------------------------------------------------------------------------------------------------
Mannitol Content                                             *****
------------------------------------------------------------------------------------------------------------------------------
</TABLE>

----------------------------------
***** Confidential portion omitted and filed separately with the Securities
      and Exchange Commission.<PAGE>

                                                                     EXHIBIT 4.1

                                    EXHIBIT D

                          HOMESEEKERS.COM, INCORPORATED

                              Common Stock Warrant
                             Expiring [Date], [2003]
                                      --------------

                                                          Date: [Date], [2000]
                                                                --------------
                  No. 1

            HOMESEEKERS.COM, INCORPORATED, a Nevada corporation (herein,
together with its successors and assigns, the "Company"), for value received,
hereby certifies that Alpha Venture Capital, Incorporated, or registered
assigns, is entitled to purchase from the Company, at any time or from time
to time prior to 5:00 p.m., New York City time, on [Date], [2003] (or such
earlier date as may be determined pursuant to Section 13 hereof),
_____________ duly authorized, validly issued, fully paid and nonassessable
shares of Common Stock, par value $.001 per share, as constituted on
[Date], [2000] (the "Common Stock"), of the Company at a purchase price of
$______ per share (subject to the adjustment in accordance with Section 2,
the "Warrant Price"), all subject to the terms, conditions and adjustments
set forth below in this Warrant.

            1      EXERCISE OF WARRANT.

            1.1    MANNER OF EXERCISE. Subject to Section 6, this Warrant may
be exercised by the holder hereof, in whole or in part, during normal
business hours on any Business Day by surrender of this Warrant to the
Company at the office of the Company maintained pursuant to Section 7.2(a),
accompanied by a subscription in substantially the form annexed hereto duly
executed by such holder and (a) by payment in cash or by certified or
official bank check payable to the order of the Company or by wire transfer
in the amount obtained by multiplying (i) the number of shares of Common
Stock (without giving effect to any adjustment therein) designated in such
subscription by (ii) the then applicable Warrant Price, (b) by instructing
the Company to withhold and cancel a number of shares of Common Stock then
issuable upon exercise of this Warrant with respect to which the excess of
the Market Price of the shares of Common Stock over the Warrant Price for
such canceled shares is at least equal to the Warrant Price for the shares
being purchased or (c) by any combination of the foregoing, whereupon such
holder shall be entitled to receive the number of duly authorized, validly
issued, fully paid and nonassessable shares of Common Stock (or Other
Securities) determined as provided in Section 2.

            1.2    WHEN EXERCISE EFFECTIVE. Any exercise of this Warrant
shall be deemed to have been effected immediately prior to the close of
business on the Business Day on which

<PAGE>

this Warrant shall have been surrendered to the Company as provided in Section
1.1, and at such time the Person or Persons in whose name or names any
certificate or certificates for shares of Common Stock (or Other Securities)
shall be issuable upon such exercise as provided in Section 1.3 shall be deemed
to have become the holder or holders of record thereof.

            1.3    DELIVERY OF STOCK CERTIFICATES, ETC. As soon as practicable
after the exercise of this Warrant, in whole or in part, and in any event
within three Business Days thereafter, the Company at its expense (including
the payment by it of any applicable issuance taxes) will cause to be issued
in the name of and delivered to the holder hereof or, subject to Section 6,
as such holder (upon payment by such holder of any applicable transfer taxes)
may direct:

                  (a) a certificate or certificates for the number of duly
     authorized, validly issued, fully paid and nonassessable shares of Common
     Stock (or Other Securities) to which such holder shall be entitled upon
     such exercise plus, in lieu of any fractional share to which such holder
     would otherwise be entitled, cash in an amount equal to the same fraction
     of the Market Price per share on the Business Day next preceding the date
     of such exercise; and

                  (b) in case such exercise is in part only, a new Warrant or
     Warrants of like tenor, calling in the aggregate on the face or faces
     thereof for issuance of the number of shares of Common Stock equal (without
     giving effect to any adjustment therein) to the number of such shares
     called for on the face of this Warrant minus the number of such shares so
     designated by such holder upon such exercise as provided in Section 1.1.

            2      CERTAIN ADJUSTMENTS TO WARRANT.

            2.1    ADJUSTMENT FOR DIVIDENDS, DISTRIBUTIONS, SUBDIVISIONS,
COMBINATIONS OR CONSOLIDATION OF COMMON STOCK.

            2.1.1. STOCK DIVIDENDS, DISTRIBUTIONS OR SUBDIVISIONS. In the event
the Company shall issue additional shares of Common Stock in a stock
dividend, stock distribution or subdivision, the Warrant Price in effect
immediately prior to such stock dividend, stock distribution or subdivision
shall, concurrently with the effectiveness of such stock dividend, stock
distribution or subdivision, be proportionately decreased.

            2.1.2. COMBINATIONS OR CONSOLIDATIONS. In the event the outstanding
shares of Common Stock shall be combined or consolidated, by reclassification
or otherwise, into a lesser number of shares of Common Stock, the Warrant
Price in effect immediately prior to such combination or consolidation shall,
concurrently with the effectiveness of such combination or consolidation, be
proportionately increased.

            2.2    ADJUSTMENT FOR MERGER OR REORGANIZATION, ETC. Subject to
the provisions of Section 13, in case of any consolidation or merger of the
Company with or into another Company or the conveyance of all, or
substantially all, of the assets of the Company to another corporation, this
Warrant shall thereafter be exercisable to purchase the number of shares of
stock or other securities or property to which a holder of the number of
shares of Common Stock

                                       2

<PAGE>

of the Company deliverable upon exercise of this Warrant would have been
entitled upon such consolidation, merger or conveyance; and, in any such case,
appropriate adjustment (as determined by the Board of Directors) shall be made
in the application of the provisions herein set forth with respect to the rights
and interest thereafter of the holder of this Warrant to the end that the
provisions set forth in Section 2.1 and this Section 2.2 (including provisions
with respect to changes in and other adjustments of the Warrant Price) shall
thereafter be applicable, as nearly as reasonably may be, in relation to any
shares of stock or other property thereafter deliverable upon the exercise of
this Warrant.

            3      NO DILUTION OR IMPAIRMENT. The Company (a) will not permit
the par value of any shares of stock receivable upon any exercise of this
Warrant to exceed the amount payable therefor upon such exercise, (b) will
take all such action as may be necessary or appropriate in order that the
Company may validly and legally issue fully paid and nonassessable shares of
stock upon each exercise of this Warrant and (c) will not take any action
that results in any adjustment of the Warrant Price if the total number of
shares of Common Stock (or Other Securities) issuable after such action, upon
any exercise of this Warrant, would exceed the total number of shares of
Common Stock (or Other Securities) then authorized by the Company's articles
of incorporation and available for the purpose of issuance upon such exercise.

           4      REPORT AS TO ADJUSTMENTS. In each case of any adjustment or
readjustment in the shares of Common Stock (or Other Securities) issuable upon
the exercise or conversion of this Warrant, the Company at its expense will
promptly compute such adjustment or readjustment in accordance with the terms of
this Warrant and prepare a report setting forth such adjustment or readjustment
and showing in detail the method of calculation thereof and the facts upon which
such adjustment or readjustment is based, including a statement of the Warrant
Price in effect immediately prior to such issuance or sale and as adjusted and
readjusted (if required by Section 2) on account thereof. The Company will
forthwith (and in any event not later than 20 days following the occurrence of
the event requiring such adjustment) furnish a copy of each such report to each
holder of this Warrant, and will, upon the written request at any time of any
holder of this Warrant, furnish to such holder a like report setting forth the
Warrant Price at the time in effect and showing how it was calculated. The
Company also will keep copies of all such reports at its principal office and at
the office or agency required to be maintained by it pursuant to Section 7.2(a),
and will cause the same to be available for inspection at each such office
during normal business hours by any holder of this Warrant or any prospective
purchaser of this Warrant designated by the holder thereof.

            5      RESTRICTIONS ON TRANSFER.

            5.1    NOTICE OF PROPOSED TRANSFER; OPINIONS OF COUNSEL. Prior to
any transfer of any Restricted Securities that are not registered pursuant to
an effective registration statement under the Securities Act (other than a
transfer pursuant to Rule 144, Rule 144A or any comparable rule under the
Securities Act), the holder thereof will give written notice to the Company
of such holder's intention to effect such transfer and to comply in all other
respects with this Section 5.1. Each such notice shall (a) describe the
manner and circumstances of the proposed transfer in sufficient detail to
enable counsel to render the opinion referred to below and (b) designate
counsel for the holder giving such notice, which counsel shall be reasonably

                                       3

<PAGE>

satisfactory to the Company. The holder giving such notice will submit a copy
thereof to the counsel designated in such notice. The following provisions shall
then apply:

                  (1) if in the written opinion of such counsel for the holder,
     obtained at the holder's sole cost and expense and a copy of which shall be
     delivered to the Company and shall be reasonably satisfactory in form,
     scope and substance to the Company, the proposed transfer may be effected
     without registration of such Restricted Securities under the Securities Act
     or applicable state securities laws, such holder shall thereupon be
     entitled to transfer such Restricted Securities in accordance with the
     terms of the notice delivered by such holder to the Company. Each
     Restricted Security or certificate, if any, issued upon or in connection
     with such transfer shall bear an appropriate restrictive legend unless, in
     the opinion of such counsel, such legend is no longer required to insure
     compliance with the Securities Act and applicable state securities laws;
     and

                  (2) if the opinion of such counsel rendered pursuant to the
     foregoing subsection (1) is not to the effect that the proposed transfer
     may legally be effected without registration of such Restricted Securities
     under the Securities Act or applicable state securities laws (such opinion
     to state the basis of the legal conclusions reached therein), such holder
     shall not be entitled to transfer such Restricted Securities (other than a
     transfer pursuant to Rule 144, Rule 144A or any comparable rule under the
     Securities Act) until receipt by the Company of a further notice and a
     further opinion of counsel for such holder to the effect stated in
     subsection (1) above or until registration of such Restricted Securities
     under the Securities Act and applicable state securities laws has become
     effective.

            5.2    TERMINATION OF RESTRICTIONS. The restrictions imposed by
this Section 5 upon the transferability of Restricted Securities shall cease
and terminate as to any particular Restricted Securities when, in the opinion
of counsel for the Company, such restrictions are no longer required in order
to ensure compliance with the Securities Act. Whenever such restrictions
shall terminate as to any Restricted Securities, the holder thereof shall be
entitled to receive from the Company, without expense (other than transfer
taxes, if any), new securities of like tenor not bearing an applicable
restrictive legend.

            6      RESERVATION OF STOCK, ETC. The Company will at all times
reserve and keep available, solely for issuance and delivery upon the
exercise of this Warrant, the number of shares of Common Stock (or Other
Securities) from time to time issuable upon the exercise of this Warrant. All
such securities shall be duly authorized and, when issued upon such exercise,
shall be validly issued and, in the case of shares, fully paid and
nonassessable with no liability on the part of the holders thereof. In
addition, the Company covenants to use reasonable best efforts to ensure that
any shares of Common Stock issuable upon the exercise of this Warrant are
registered pursuant to an effective registration statement under the
Securities Act. If the shares of Common Stock (or Other Securities) issuable
upon the exercise of this Warrant are not registered pursuant to an effective
registration statement under the Securities Act, the Company shall be under
no obligation to issue such securities unless the holder of this Warrant
presents satisfactory evidence to the Company that (a) such holder is, at the
time of exercise of this Warrant, an "accredited investor," as such term is
defined in Rule 501(a) of Regulation D promulgated under the Securities Act,
or (b) such shares of Common Stock (or Other Securities)

                                       4

<PAGE>

may be issued to such holder pursuant to another available exemption from the
registration requirements of the Securities Act.

            7      OWNERSHIP TRANSFER AND SUBSTITUTION OF WARRANTS.

            7.1    OWNERSHIP OF WARRANTS. The Company may treat the Person in
whose name this Warrant is registered on the register kept at the principal
office of the Company as the owner and holder thereof for all purposes,
notwithstanding any notice to the contrary, except that, if and when this
Warrant is properly assigned in blank, the Company may (but shall not be
obligated to) treat the bearer thereof as the owner of such Warrant for all
purposes, notwithstanding any notice to the contrary. This Warrant, if
properly assigned, may be exercised by a new holder without first having a
new Warrant issued.

            7.2    OFFICE; TRANSFER AND EXCHANGE. (a) The Company will maintain
its principal office in Reno, Nevada or at such other location as it
designates in a written notice delivered to each registered holder of this
Warrant prior to any change of such location, and all notices, presentations
and demands in respect of this Warrant may be made upon it at such location.
The Company may designate from time to time by notice to the registered
holder of this Warrant an office or agency of the Company where such notices,
presentations and demands in respect of this Warrant may be made in lieu of
the Company's principal office.

            (b) Upon any surrender of this Warrant, properly endorsed, for
registration of transfer or for exchange at the principal office of the
Company or the office of the Company maintained pursuant to Section 7.2(a),
the Company at its expense will (subject to compliance with Section 5, if
applicable) execute and deliver to or upon the order of the holder thereof a
new Warrant or Warrants of like tenor, in the name of such holder or as such
holder (upon payment by such holder of any applicable transfer taxes) may
direct, calling in the aggregate on the face or faces thereof for the number
of shares of Common Stock called for on the face or faces of the Warrant or
Warrants so surrendered.

            7.3    REPLACEMENT OF WARRANTS. Upon receipt of evidence reasonably
satisfactory to the Company of the loss, theft, destruction or mutilation of any
Warrant (which may be a written statement as to such loss, theft, destruction or
mutilation) and (a) in the case of such loss, theft or destruction of any
Warrant, upon delivery of indemnity reasonably satisfactory to the Company in
form and amount, or (b) in the case of any such mutilation, upon surrender of
such Warrant for cancellation at the office of the Company maintained pursuant
to Section 7.2(a) or the principal office of the Company, the Company at its
expense will execute and deliver, in lieu thereof, a new Warrant of like tenor.

            8      DEFINITIONS. As used herein, unless the context otherwise
requires, the following terms have the following respective meanings:

            "BUSINESS DAY" shall mean any day other than a Saturday, Sunday or
any other day on which U.S. Federal Reserve member banks are not open for
business in New York, New York.

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

                                       5

<PAGE>

            "COMPANY" shall have the meaning specified in the opening
paragraphs of this Warrant, including any corporation that shall succeed to
or assume the obligations of the Company hereunder in compliance with Section
2.2.

            "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, or
any similar Federal statute, and the rules and regulations of the Commission
thereunder, all as the same shall be in effect at the time.

            "MARKET PRICE" shall mean, per share of Common Stock that the
holders of this Warrant shall be entitled to receive upon exercise hereof, on
any date specified herein, (a) the closing price per share of Common Stock on
the Nasdaq SmallCap Market or such other principal automated quotation system
or national securities exchange on which the Common Stock is then quoted or
listed, as reported in THE WALL STREET JOURNAL, or (b) if (a) is
inapplicable, a price per share thereof equal to the fair value thereof
determined in good faith by a resolution of the Board of Directors of the
Company as of a date that is within 15 days of the date as of which the
determination is to be made.

            "OTHER SECURITIES" shall mean any stock (other than Common Stock)
and other securities of the Company or any other Person (corporate or
otherwise) that the holder of this Warrant at any time shall be entitled to
receive, or shall have received, upon the exercise of this Warrant, in lieu
of or in addition to Common Stock, or that at any time shall be issuable or
shall have been issued in exchange for or in replacement of Common Stock or
Other Securities pursuant to Section 2 or otherwise.

            "PERSON" shall mean a corporation, an association, a partnership,
an organization or business, an individual, a government or political
subdivision thereof or a governmental agency.

            "RESTRICTED SECURITIES" shall mean any (a) shares of Common Stock
issuable upon exercise of this Warrant that are not registered pursuant to an
effective registration statement under the Securities Act or (b) Other
Securities issued subsequent to any exercise of this Warrant as a dividend or
other distribution with respect to, or resulting from a subdivision of the
outstanding Other Securities into a greater number of shares by
reclassification, stock splits or otherwise, or in exchange for or in
replacement of Other Securities issued upon such exercise, which are
evidenced by a certificate or certificates bearing an applicable restrictive
legend.

            "SECURITIES ACT" shall mean the Securities Act of 1933, or any
similar Federal statute, and the rules and regulations of the Commission
thereunder, all as the same shall be in effect at the time.

            "WARRANT" shall have the meaning specified in the opening
paragraphs of this Warrant.

            "WARRANT PRICE" shall have the meaning specified in the opening
paragraphs of this Warrant.

            9      REMEDIES. The Company stipulates that the remedies at law
of the holder of this Warrant in the event of any default or threatened
default by the Company in the

                                       6

<PAGE>

performance of or compliance with any of the terms of this Warrant are not and
will not be adequate, and that, to the extent permitted by applicable law, such
terms may be specifically enforced by a decree for the specific performance of
any agreement contained herein or by an injunction against a violation of any of
the terms hereof or otherwise.

            10     NO RIGHTS OR LIABILITIES AS STOCKHOLDER. Nothing contained
in this Warrant shall be construed as conferring upon any holder hereof any
rights as a stockholder of the Company or as imposing any obligation on such
holder to purchase any securities or as imposing any liabilities on such
holder as a stockholder of the Company, whether such obligation or
liabilities are asserted by the Company or by creditors of the Company.

            11     NOTICES. All notices and other communications provided for
herein shall be delivered or mailed by first class mail, postage prepaid,
addressed (a) if to any holder of this Warrant, at the registered address of
such holder as set forth in the register kept by the Company, or (b) if to
the Company, at its principal office, 6490 South McCarran Boulevard, Suite
D-28, Reno, Nevada 89509, or at the address of such other principal office of
the Company as the Company shall have furnished to each holder of this
Warrant in writing; PROVIDED, HOWEVER, that the exercise of any Warrant shall
be effective in the manner provided in Section 1.

            12     MISCELLANEOUS. This Warrant and any term hereof may be
changed, waived, discharged or terminated only by an instrument in writing
signed by the party against which enforcement of such change, waiver,
discharge or termination is sought. Any provision of this Warrant that shall
be prohibited or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions hereof, and
any such prohibition or unenforceability in any jurisdiction shall not
invalidate or render unenforceable such provision in any other jurisdiction.
To the extent permitted by applicable law, the Company waives any provision
of law that shall render any provision hereof prohibited or unenforceable in
any respect. This Warrant shall be governed by the substantive laws of the
State of Nevada without reference to the choice of law rules thereof. The
headings of this Warrant are inserted for convenience only and shall not be
deemed to constitute a part hereof.

            13     EXPIRATION. Subject to the provisions in Section 1.1 hereof,
the right to exercise this Warrant shall expire at 5:00 p.m., New York City
time, on the date set forth on the first page hereof.

           [The remainder of this page is intentionally left blank.]

                                       7

<PAGE>

                  IN WITNESS WHEREOF, the Company has caused this Warrant to be
exercised by its officer thereunto duly authorized as of the date first written
above.

                                     HOMESEEKERS.COM INCORPORATED

                                      By:
                                            ------------------------------------
                                      Name:
                                            ------------------------------------
                                      Title:
                                            ------------------------------------

                                       8

<PAGE>

                              FORM OF SUBSCRIPTION

     THE EXERCISE OF THIS WARRANT IS SUBJECT TO, AND SHALL ONLY BE EFFECTIVE
UPON, SATISFACTION OF ANY CONDITIONS SET FORTH IN SECTION 6 OF THIS WARRANT AND
ANY APPLICABLE REGULATORY FILING REQUIREMENTS SUCH AS THE PREMERGER NOTIFICATION
AND REPORT FORM FILING REQUIREMENTS OF THE HART-SCOTT-RODINO ANTITRUST
IMPROVEMENTS ACT OF 1976 AND REGULATIONS PROMULGATED PURSUANT THERETO.

                 [To be executed only upon exercise of Warrant]

To HOMESEEKERS.COM, INCORPORATED

     The undersigned registered holder of the attached Warrant hereby
irrevocably exercises such Warrant for, and purchases thereunder,
_______ (1) shares of Common Stock of HOMESEEKERS.COM, INCORPORATED, and
herewith makes payment as follows (check as applicable): /_/ certified or
official bank check in the amount of $_________; /_/ wire transfer in the
amount of $_________; and/or /_/ cancellation of _______ shares of Common
Stock otherwise issuable under the Warrant. The undersigned requests that the
certificates for such shares be issued in the name of, and delivered to
____________________________, whose address is _______________________________
______________________________.

Dated:
         ---------------------------

                             ---------------------------------------------------
                             (Signature must conform in all respects to name of
                             holder as specified on the face of Warrant)

                             ---------------------------------------------------
                             (Street Address)

                             ---------------------------------------------------
                             (City)                  (State)          (Zip Code)

--------
(1)      Insert here the number of shares called for on the face of this Warrant
         (or in the case of a partial exercise, the portion thereof as to which
         this Warrant is being exercised), in either case without making any
         adjustment for additional Common Stock or any other stock or other
         securities or property or cash that, pursuant to the adjustment
         provisions of this Warrant, may be delivered upon exercise. In the case
         of a partial exercise, a new Warrant or Warrants will be issued and
         delivered, representing the unexercised portion of the Warrant, to the
         holder surrendering the Warrant.

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