Immunomedics, Inc.
                               300 American Road
                             Morris Plains, NJ 07950
                                  973-605-8200



                                 January 7, 2000


The Aries Master Fund
The Aries Domestic Fund, L.P.
The Aries Domestic Fund II, L.P.
Lindsay A. Rosenwald, M.D.
Mark C. Rogers, M.D.
Wayne Rothbaum
c/o Paramount Capital Asset Management, Inc.
787 7th Avenue, 48th Floor
New York, NY  10019

Attention:  David M. Tanen

Gentlemen:

This  letter is written to confirm  our  understanding  with  respect to certain
matters addressed in the Common Stock Purchase  Agreement,  dated as of December
14, 1999 (the  "Agreement"),  among us. Terms that are not otherwise  defined in
this letter have the same meanings as in the Agreement.

We have agreed to delete the first  sentence of Section 7.7 of the Agreement and
to insert in its place the following language:

"Without  the prior  consent of the  Purchasers,  the  Company  may not sell its
business  (either by way of a sale or  transfer  of assets,  sale or transfer of
stock, merger or otherwise) to any person or entity that is, prior to such sale,
an  "Affiliate"  of the Company,  unless such transfer is for  consideration  at
least equal to (a) the Fair  Market  Value in the event of a sale or transfer of
assets or (b) the then  Current  Market Price in the event of a sale or transfer
of stock.  The "Fair  Market  Value" of any asset of the Company  means the fair
market  value  thereof as  determined  in good faith by the  Company's  Board of
Directors.  The then "Current  Market Price" per share shall be deemed to be the
last sale price of the Common  Stock on the  trading  date prior to such sale or
transfer or, in case no such  reported sale takes place on such day, the average
of the last  reported  bid and asked  prices of the Common Stock on such day, in
either case on the principal  national  securities  exchange on which the Common
Stock is admitted to trading or listed,  or if not listed or admitted to trading
on any such exchange,  the representative  closing bid price of the Common Stock
as reported by the National Association of Securities Dealers, Inc. Automated

<PAGE>

Quotation  System  ("Nasdaq"),  or other  similar  organization  if Nasdaq is no
longer  reporting such  information,  or, if the Common Stock is not reported on
Nasdaq,   the  high  per  share  bid   price  for  the   Common   Stock  in  the
over-the-counter  market as reported by the National Quotation Bureau or similar
organization,  or if not so available, the fair market value of the Common Stock
as determined in good faith by the Company's Board of Directors. For purposes of
this Agreement,  the term "Affiliate"  means any person or entity that controls,
is controlled by or is under common control with the Company."

We further agree that the change  described above  represents the only change to
the  Agreement  and the remaining  provisions  contained in the Agreement  shall
remain unchanged and in effect.


Kindly  acknowledge  your  agreement  with the terms of this  letter by  signing
below.

Very truly yours,

IMMUNOMEDICS, INC.


By: /s/David M. Goldenberg, M.D.
_________________________________
      David M. Goldenberg, M.D.
      Chairman and Chief Executive Officer

DMG:wjh
Enclosures

Acknowledged and agreed to:

THE ARIES MASTER FUND


By: /s/ Lindsay A. Rosenwald, M.D.
_________________________________

                                      -2-
<PAGE>

THE ARIES DOMESTIC FUND, L.P.


By: /s/ Lindsay A. Rosenwald, M.D.
_________________________________

THE ARIES DOMESTIC FUND II, L.P.


By: /s/ Lindsay A. Rosenwald, M.D.
_________________________________

/s/ Lindsay A. Rosenwald, M.D.
-------------------------------------
Lindsay A. Rosenwald, M.D.

/s/ Marc C. Rogers, M.D.
-------------------------------------
Mark C. Rogers, M.D.


-------------------------------------
Wayne Rothbaum


                                      -3-
<PAGE>


                                    COMMON  STOCK   PURCHASE   AGREEMENT   (this
                           "Agreement")  dated as of December 14,  1999,  by and
                           among IMMUNOMEDICS, INC., a Delaware corporation (the
                           "Company"),  and the  PURCHASERS  listed on Exhibit A
                           ("Purchasers").

                  The  Company  desires  to issue  and sell to  Purchasers,  and
Purchasers desire to purchase from the Company,  shares (the "Common Shares") of
the Company's common stock,  par value $.01 per share (the "Common  Stock"),  at
$3.00 per share  (the  "Per  Share  Price")  upon and  subject  to the terms and
conditions of this Agreement.

                  Accordingly,  in  consideration of the premises and the mutual
agreements  contained  herein,  and for other good and  valuable  consideration,
Purchasers and the Company agree as follows:

                  1.       Purchase of Company Securities.

                  1.1.  Purchase and Sale of the Common  Shares.  (a) Subject to
the terms and conditions of this Agreement, (i) the Company shall issue and sell
to Purchasers,  and Purchasers,  severally and not jointly,  shall purchase from
the  Company,  2,500,000  shares  of  Common  Stock as set  forth on  Exhibit  A
(allocated  among the  Purchasers  as set forth on Exhibit  A).  Such  shares of
Common Stock are  hereinafter  sometimes  referred to as the  "Securities."  The
aggregate  purchase  price  for the  Common  Shares  shall  be  $7,500,000  (the
"Aggregate  Purchase  Price")  (allocated  among the  Purchasers as set forth on
Exhibit A).

                  2.       Closing.

                  2.1.  Closing.  The  closing of the  purchase  and sale of the
Common  Shares shall take place at a single  closing at the offices of Paramount
Capital Asset Management, Inc. ("Paramount"), at 787 Seventh Avenue, 48th Floor,
New York,  New  York,  10019.  Such  closing  (the  "Closing")  will take  place
contemporaneously with the execution and delivery of this Agreement. The date of
the Closing is referred to as the "Closing  Date." At the  Closing,  the Company
will deliver to Purchasers  the Common Shares  against  payment of the Aggregate
Purchase Price by Purchasers by wire transfer payable to the Company pursuant to
the  instructions  attached  hereto as  Exhibit B. The  Common  Shares  shall be
registered  in  Purchasers'  names  in such  denominations  as are set  forth on
Exhibit A annexed hereto.

                  3. Conditions to the Obligations of Purchasers at the Closing.
The  obligation  of  Purchasers  to purchase and pay for the Common Shares to be
purchased  by  Purchasers  at the Closing is subject to the  satisfaction  on or
prior to the Closing Date of the following conditions,  which may only be waived
by written consent of Purchasers:

                  3.1. Opinion of Counsel to the Company.  Purchasers shall have
received from Lowenstein Sandler PC, counsel for the Company,  its opinion dated
the Closing Date in the form of Exhibit C.

<PAGE>

                  3.2. Representations  and  Warranties.  All  of the
representations  and warranties of the Company contained in this Agreement shall
be true and correct at and as of the Closing Date.

                  3.3.  Performance  of  Covenants.  All  of the  covenants  and
agreements of the Company  contained in this Agreement  required to be performed
on or  prior  to  the  Closing  Date  shall  have  been  performed  in a  manner
satisfactory in all respects to Purchasers.

                  3.4. Legal Action. No injunction, order, investigation, claim,
action or proceeding  before any court or governmental  body shall be pending or
threatened  wherein an  unfavorable  judgment,  decree or order would  restrain,
impair or prevent the carrying out of this Agreement or any of the  transactions
contemplated  thereby,  declare unlawful the  transactions  contemplated by this
Agreement or cause any such transaction to be rescinded.

                  3.5.  Consents.  The Company shall have obtained in writing or
made  all  consents,   waivers,   approvals,   orders,  permits,   licenses  and
authorizations of, and registrations,  declarations,  notices to and filings and
applications  with, any governmental  authority or any other Person  (including,
without limitation, securityholders and creditors of the Company) required to be
obtained  or made in order to enable the  Company to observe and comply with all
of its  obligations  under this  Agreement  and to  consummate  and  perform the
transactions  contemplated  hereby.  The Board of Directors of the Company shall
have taken all action required to permit the  transactions  contemplated by this
Agreement.

                  3.6.   Closing Documents.  The Company shall have delivered to
Purchasers the following:

                  (a) a  certificate  executed  on behalf of the  Company by the
Chairman  and Chief  Executive  Officer of the Company  dated the  Closing  Date
stating  that the  conditions  set forth in  Sections  3.2 through 3.5 have been
satisfied;

                  (b) a certificate  of the Secretary of the Company,  dated the
Closing Date, as to the continued and valid existence of the Company, certifying
the  attached  copy of the  By-laws of the  Company,  the  authorization  of the
execution,  delivery and  performance  of this  Agreement,  and the  resolutions
adopted by the Board of Directors of the Company  authorizing  the actions to be
taken by the Company under this Agreement;

                  (c) a  certificate  of the  Secretary of State of the State of
Delaware,  dated a  recent  date,  to the  effect  that the  Company  is in good
standing in the State of Delaware and that all annual reports, if any, have been
filed as required and, if readily  available  that all franchise  taxes and fees
have been paid in connection therewith;

                  (d) a certified copy of the  Certificate of  Incorporation  of
the  Company  as filed  with the  Secretary  of State of the State of  Delaware,
including any amendments thereto; and

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<PAGE>

                  (e) such  certificates,  other  documents and  instruments  as
Purchasers and their counsel may reasonably  request in connection  with, and to
effect, the transactions contemplated by this Agreement.

                  3.7. Proceedings. All corporate and other proceedings taken or
to be taken in connection with the  transactions  contemplated by this Agreement
to be  consummated at such Closing and all documents  incident  thereto shall be
satisfactory in form and substance to Purchasers.

                  3.8. Closing Financial Statements; Absence of Changes. (a) The
Company shall have provided to Purchasers  (i) the unaudited  balance  sheets of
the Company as of September 30, 1999,  and the related  unaudited  statements of
operations, and cash flows for the three-month period then ended (the "Financial
Statements"),  all of which will be correct and complete and will present fairly
the financial position of the Company and the results of its operations and cash
flows as of the time and for the periods  then  ended,  provided  adjusting  and
closing  entries  ordinarily  made at the close of any such period in connection
with audit,  and footnote  information,  are omitted,  and (ii) the  unqualified
certification,  in form and substance  satisfactory to Purchasers,  of the Chief
Financial Officer of the Company, acting on behalf of the Company, to the effect
that the Financial  Statements  have been prepared in accordance  with the books
and records of the Company and generally accepted accounting  principles applied
on a basis  consistent  with prior years (except as otherwise  specified in such
certification), and present fairly the financial position of the Company and the
results of its  operations  cash flows as of the time and for the  periods  then
ended,  provided  adjusting and closing entries  ordinarily made at the close of
any such period in connection with audit, and footnote information, are omitted.

                  (b) Except as set forth on the schedules to this  Agreement or
as previously publicly disclosed,  and except for net losses consistent in scope
with net losses  incurred by the Company during the nine months ended  September
30,  1999,  there shall have been no material  adverse  change in the  business,
financial  condition,  operating  results,  employee  or customer  relations  or
prospects of the Company, from September 30, 1999 to the Closing Date.

                  3.9. Schedules.  The Company shall have provided to Purchasers
all schedules  required  pursuant to this  Agreement,  which  schedules shall be
satisfactory to Purchasers in their sole discretion.

                  3.10. Material Agreements.  The Company shall have provided to
the  Purchasers  a copy of  agreements  entered by and among the Company and all
holders of its  Series F  Convertible  Preferred  Stock  pursuant  to which such
holders have agreed that the Company may redeem all outstanding shares of Series
F Preferred  Stock at any time on or before  December 31, 1999, at a price equal
to 109% of the stated value of such Series F Convertible  Preferred Stock (which
is $10,000).

                  4.  Conditions  to  the  Obligations  of  the  Company  at the
Closings.  The  obligation of the Company to issue and sell the Common Shares to
the Purchasers at the Closing is subject to the  satisfaction on or prior to the
Closing  Date of the  following  conditions,  any of which  may be waived by the
Company:

                                       3
<PAGE>

                  4.1.  Representations and Warranties.  The representations and
warranties of Purchasers  contained in this Agreement  shall be true and correct
at and as of the Closing Date.

                  4.2. Legal Action. No injunction, order, investigation, claim,
action or proceeding  before any court or governmental  body shall be pending or
threatened  wherein an  unfavorable  judgment,  decree or order would  restrain,
impair or prevent the carrying out of this Agreement or any of the  transactions
contemplated  hereby,  declare unlawful the transactions  contemplated hereby or
cause any such transaction to be rescinded.

                  4.3  Performance  of  Covenants.  All  of  the  covenants  and
agreements  of  the  Purchasers  contained  in  this  Agreement  required  to be
performed on or prior to the Closing Date shall have been  performed in a manner
satisfactory in all respects to the Company.

                  5.   Representations  and  Warranties  of  the  Company.   The
representations  and warranties of the Company  contained  herein are subject to
and qualified by the disclosures made in the Company's most recent Annual Report
on Form 10-K and  Quarterly  Report on Form  10-Q,  as filed  with the SEC.  The
Company hereby  represents and warrants to each Purchaser as of the Closing Date
as follows:

                  5.1.   Organization.   The  Company  is  a  corporation   duly
organized,  validly existing and in good standing under the laws of the State of
Delaware.  The Company is eligible  to be treated as a C  corporation  under the
Internal  Revenue  Code of 1986,  as amended (the  "Code").  The Company has all
requisite  corporate  power and authority,  and holds all licenses,  permits and
other  required  authorizations  from  governmental  authorities,  necessary  to
conduct its business as now being  conducted and to own or lease the  properties
and  assets  now owned or held  under  license  or lease.  The  Company  is duly
qualified  or licensed  and in good  standing as a foreign  corporation  in each
jurisdiction  wherein  the  character  of its  properties  or the  nature of the
activities  conducted by it makes such  qualification  or  licensing  necessary,
except where the failure to so qualify would not have a material  adverse effect
on the Company.

                  5.2. Charter Documents.  The Company has heretofore  delivered
to  Purchasers  true,   correct  and  complete  copies  of  the  Certificate  of
Incorporation  and  By-Laws  (or  comparable  organizational  documents)  of the
Company as in full force and effect on the date hereof.

                  5.3.  Capitalization.  As of December 10, 1999,  the Company's
authorized  capitalization  consists of 70,000,000  shares of Common  Stock,  of
which  43,655,709  shares are issued and outstanding,  and 10,000,000  shares of
preferred  stock, par value $.01 per share, of which 595.5 shares are designated
as  Series  F  Convertible  Preferred  Stock  and are  issued  and  outstanding.
15,022,288  shares of Common Stock are reserved for issuance upon the conversion
or exercise of  convertible  securities,  options,  warrants or other  rights to
purchase  Common  Stock  outstanding  as of the Closing  Date.  All  outstanding
securities  of the  Company are validly  issued,  fully paid and  nonassessable.
Except  for  the  rights  of  the  Series  F  Convertible  Preferred  Stock,  no
stockholder of the Company is entitled to any preemptive  rights with respect to
the purchase or sale of any securities by the Company.  There are no outstanding
options, warrants or other rights, commitments or arrangements, written or oral,
to purchase or otherwise  acquire any authorized but unissued  shares of capital
stock of the Company or any security directly or indirectly  convertible into or
exchangeable  for any  capital  stock of the  Company  or under  which  any such
option,  warrant or  convertible  security  may be issued in the  future  except
otherwise  as set  forth  on  Schedule  5.3.  There  are  no  voting  trusts  or
agreements,  stockholders'  agreements,  pledge agreements,  buy-sell, rights of

                                       4
<PAGE>

first offer,  negotiation or refusal or proxies or similar arrangements relating
to any  securities  of the Company to which the  Company is a party,  and to the
best  knowledge of the Company after due inquiry there are no other such trusts,
agreement,  rights,  proxies  or  similar  arrangements,  except as set forth on
Schedule 5.3.  Except as otherwise set forth on Schedule 5.3 or as  contemplated
by this  Agreement,  none of the  shares  of  capital  stock of the  Company  is
reserved for any purpose,  and the Company is neither  subject to any obligation
(contingent or otherwise), nor has any option to repurchase or otherwise acquire
or retire any shares of its capital stock.

                  5.4 Due Authorization,  Valid Issuance, Etc. The Common Shares
to be purchased on the Closing Date have been duly  authorized  and, when issued
in accordance with this Agreement upon the Closing Date, will be validly issued,
fully paid and non-assessable and will be free and clear of all liens imposed by
or through the  Company,  subject  only to  restrictions  set forth  herein,  as
applicable,  or applicable federal and state securities laws. The issuance, sale
and clear  delivery of such Common Shares will not be subject to any  preemptive
right of  stockholders  of the Company or to any right of first refusal or other
right in favor of any  person or entity  except for  provisions  which have been
waived in writing (and as to which the  Purchasers  have  received a copy of) or
satisfied and as set forth on Schedule 5.4. The Company's executive officers and
directors have studied and fully  understand the nature of the securities  being
sold hereunder, and recognize that they have a potential dilutive effect. Except
as set forth on Schedule 5.4, no  anti-dilution  adjustments with respect to the
outstanding  securities  of the Company will be triggered by the issuance of the
securities contemplated hereby.

                  5.5.  Subsidiaries.  Except  as  otherwise  disclosed  in  the
Company's  Annual  Report on Form 10-K for the year  ended  June 30,  1999,  the
Company has no wholly or  partially  owned  Subsidiaries  (as defined in Section
9.9) and does not  control,  directly  or  indirectly,  any  other  corporation,
business  trust,  firm,  partnership,  association,  joint  venture,  entity  or
organization.  Except as otherwise  disclosed in the Company's  Annual Report on
Form 10-K for the year ended June 30, 1999,  the Company does not own any shares
of stock,  partnership  interest,  joint venture interest or any other security,
equity or interest in any other corporation or other Person.

                  5.6.  Authorization;  No  Breach.  The  Company  has the  full
corporate power and authority to execute,  deliver and enter into this Agreement
and to perform  its  obligations  hereunder,  and the  execution,  delivery  and
performance of this  Agreement and all other  transactions  contemplated  hereby
have been duly  authorized by the Company.  This Agreement  constitutes a legal,
valid and binding obligation of the Company,  enforceable in accordance with its
terms  except  as  such   enforceability  may  be  limited  by  (a)  bankruptcy,
insolvency,  moratorium and similar laws affecting  creditors'  rights generally
and (b) the availability of remedies under general equitable principles.  Except

                                       5
<PAGE>

as set forth on Schedule  5.6, the execution and delivery by the Company of this
Agreement,  the  offering,  sale and  issuance  of the  Common  Shares,  and the
performance and fulfillment by the Company of its obligations hereunder,  do not
and will not (i) conflict with or result in a breach of the terms, conditions or
provisions of, (ii) constitute a default under,  or event which,  with notice or
lapse of time or both,  would  constitute  a breach of or default  under,  (iii)
result in the creation of any lien, security interest,  adverse claim, charge or
encumbrance  upon the capital  stock or assets of the Company  pursuant to, (iv)
give any third party the right to accelerate any obligation  under or terminate,
(v)  result  in a  violation  of,  (vi)  result  in the  loss  of  any  license,
certificate,  legal privilege or legal right enjoyed or possessed by the Company
under,  or (vii) with the  exception of an  application  to NASDAQ,  require any
authorization,  consent, approval, exemption or other action by or notice to any
court or  administrative or governmental body pursuant to or require the consent
of any other Person under,  the Certificate of  Incorporation  or By-Laws of the
Company or any law, statute,  rule or regulation to which the Company is subject
or by which any of its  properties  are  bound,  or any  agreement,  instrument,
order,  judgment  or decree  to which the  Company  is  subject  or by which its
properties  are  bound,  except,  in all  instances,  for  matters  which do not
materially adversely affect the Company's business,  financial condition, result
of operations or prospects ("Material Adverse Effect").

                  5.7. No Material  Adverse  Changes.  Since September 30, 1999,
except as  disclosed on Schedule 5.7 there has not at any time been any material
adverse change in the business, financial condition, operating results, business
prospects,  employee relations or customer  relations of the Company.  Except as
set forth on Schedule 5.7, no event or circumstance  has occurred or exists with
respect to the Company or its  business,  properties,  prospects,  operations or
financial condition,  which, under applicable law, rule or regulation,  requires
public  disclosure  or  announcement  by the  Company  but which has not been so
publicly announced or disclosed.

                  5.8. Absence of Certain  Developments.  Except as contemplated
by this Agreement,  and except as set forth on Schedule 5.8, since September 30,
1999 the Company has not,  nor will have prior to the Closing  Date:  (a) issued
any  securities  (other than as permitted or  contemplated  by this Agreement or
securities issued subsequent to December 10, 1999 upon conversion of outstanding
securities or options); (b) borrowed any amount or incurred or became subject to
any liabilities  (absolute or contingent)  which involve $50,000 or more,  other
than  liabilities  incurred in the ordinary  course of business and  liabilities
under contracts entered into in the ordinary course of business;  (c) discharged
or satisfied any lien,  adverse claim or  encumbrance  or paid any obligation or
liability  (absolute or contingent),  other than current liabilities paid in the
ordinary course of business; (d) declared or made any payment or distribution of
cash or other  property to the  stockholders  of the Company with respect to the
Common Stock or purchased or redeemed any shares of Common Stock; (e) mortgaged,
pledged  or  subjected  to  any  lien,  adverse  claim,   charge  or  any  other
encumbrance, any of its properties or assets, except for liens for taxes not yet
due and payable and  transactions in the ordinary course of business;  (f) sold,
assigned or transferred any of its assets, tangible or intangible, except in the
ordinary  course of business or in an amount less than $50,000,  or disclosed to
any person, firm or entity not subject to a confidentiality  obligation with the
Company any proprietary confidential information; (g) suffered any extraordinary
losses or waived any rights of material value; (h) made any capital expenditures
or commitments therefor greater than $50,000 in the aggregate;  (i) entered into
any other  transaction  other than in the ordinary course of business;  (j) made
any charitable  contributions or pledges;  (k) suffered damages,  destruction or
casualty  loss,  whether  or not  covered  by  insurance,  affecting  any of the

                                       6
<PAGE>
properties  or assets of the  Company or any other  properties  or assets of the
Company which could have a material  adverse  effect on the business,  financial
condition, operating results, employee or customer relations or prospects of the
Company;  (l) made any  material  change  in the  nature  or  operations  of the
business of the Company;  or (m)  resolved to or entered  into any  agreement or
understanding with respect to any of the foregoing.

                  5.9. Properties.  The Company has good and marketable title to
all of the real  property  and good title to all of the  personal  property  and
assets it purports to own as set forth in the Financial Statements, whether such
property  is real or  personal,  free and clear of all  liens,  adverse  claims,
charges,  encumbrances or restrictions of any nature whatsoever, except (a) such
as are reflected on Schedule 5.9 or in the notes to the Financial  Statements in
the Company's  Annual Report on Form 10-K for the year ended June 30, 1999,  (b)
for  receivables and charges  collected in the ordinary course of business,  (c)
liens  with  respect  to taxes not yet due and (d)  immaterial  exceptions  of a
routine and customary  nature.  Except as disclosed in Schedule 5.9, the Company
owns or leases all such  properties  as are  necessary to its  operations as now
conducted and as presently proposed to be conducted and all such properties are,
in all material respects, in good operating condition and repair.

                  5.10. Taxes. Except as set forth on Schedule 5.10, the Company
has timely filed all federal,  state,  local and foreign tax returns and reports
required to be filed, and all taxes, fees,  assessments and governmental charges
of any nature  shown by such returns and reports to be due and payable have been
timely paid except for those amounts being contested in good faith and for which
appropriate  amounts have been reserved in accordance  with  generally  accepted
accounting principles. There is no tax deficiency that has been, or, to the best
knowledge of the Company after due inquiry may reasonably be,  asserted  against
the Company that would  materially  adversely affect the business or operations,
or proposed  business or  operations,  of the Company.  All such tax returns and
reports were prepared in accordance  with the relevant rules and  regulations of
each  taxing  authority  having  jurisdiction  over the Company and are true and
correct  in all  material  respects.  The  Company  has  neither  given nor been
requested  to give any waiver of any  statute  of  limitations  relating  to the
payment of federal,  state,  local or foreign  taxes.  The Company has not been,
nor, to its knowledge,  is it now being, audited by any federal, state, local or
foreign tax  authorities.  The Company has made all required  deposits for taxes
applicable  to the current tax year.  The Company is not,  and has never been, a
member of any "affiliated group" within the meaning of Section 1504 of the Code,
as in effect from time to time.

                  5.11. Litigation.  Except as set forth on Schedule 5.11, there
are no actions, suits, proceedings, orders, investigations or claims pending or,
to the best  knowledge of the Company after due inquiry,  threatened  against or
affecting the Company,  at law or in equity or before or by any federal,  state,
municipal or other governmental department, commission, board, bureau, agency or
instrumentality;  there are no arbitration  proceedings pending under collective
bargaining agreements or otherwise.

                  5.12.  Compliance  with Law.  The Company has  complied in all
material  respects with all  applicable  statutes and  regulations of the United
States and of all states,  municipalities  and  applicable  agencies and foreign
jurisdictions  or  bodies  in  respect  of  the  conduct  of  its  business  and
operations.

                                       7
<PAGE>

                  5.13.  Trademarks and Patents.  Schedule 5.13 contains a true,
complete and correct list of all registered,  certificated or issued trademarks,
trade names, patents and copyrights (and applications  therefor),  if any, owned
or (to the extent evidenced by contract or license  agreement)  licensed or used
or  required  to be used by the  Company as of or prior to the  Closing  Date in
connection  with its business and,  except as set forth on Schedule  5.13,  each
such  trademark,  trade name,  patent and copyright (and  application  therefor)
listed in  Schedule  5.13 as being  owned by the  Company is not  subject to any
license,  royalty  arrangement,  option or dispute  and is free and clear of all
material liens. To the best knowledge of the Company after due inquiry,  none of
the  trademarks,  trade  names,  patents or  copyrights  used by the  Company in
connection  with its business  infringes any  trademark,  trade name,  patent or
copyright  of others in the United  States or in any other  country,  in any way
which materially  adversely  affects or which in the future is reasonable likely
to materially adversely affect the business or operations of the Company. Except
as set forth on Schedule 5.13 or in the Company's Annual Report on Form 10-K for
the year ended June 30, 1999, no stockholder, officer or director of the Company
or any other  person  owns or has any  interest  in any  trademark,  trade name,
service  mark,  patent,  copyright or  application  therefor,  or trade  secret,
licenses,  invention,  information or proprietary right or process, if any, used
by the Company in  connection  with its  business.  The Company has no notice or
knowledge of any objection or claim being asserted by any person with respect to
the ownership,  validity,  enforceability  or use of any such trademarks,  trade
names,  patents and copyrights (and  applications  therefor)  listed on Schedule
5.13 or challenging or questioning the validity or  effectiveness of any license
relating thereto.  There are no unresolved conflicts with, or pending claims of,
any other person, whether in litigation or otherwise,  involving the trademarks,
trade names, patents and copyrights (and applications  therefor),  and there are
no liens,  encumbrances,  adverse  claims,  or rights of any other  person which
would prevent the Company from fulfilling its  obligations  under this Agreement
except in all cases which would not have a Material Adverse Effect.  To the best
knowledge  of the Company  after due inquiry,  the  business of the Company,  as
presently  conducted does not cause the Company to violate any trademark,  trade
name, patent,  copyright,  trade secret,  license or proprietary interest of any
other  person or  entity,  in any way which  materially  adversely  affects  the
business or operations of the Company. Except as disclosed in Schedule 5.13, the
Company  possesses all proprietary  technology  necessary for the conduct of its
business.

                  5.14.  Insurance.  Each of the Company's insurance policies is
in full force and  effect;  and the  Company  is not in default in any  material
respect with respect to its  obligations  under any of such insurance  policies.
Such insurance coverage is in amounts not less than is customarily maintained by
corporations  engaged in the same or similar  business and  similarly  situated,
including,  without  limitation,  insurance against loss,  damage,  fire, theft,
public  liability and other risks.  The activities and operations of the Company
have been conducted in a manner so as to conform to all applicable provisions of
these  insurance  policies  and the  Company has not taken or failed to take any
action which would cause any such insurance policy to lapse.

                  5.15.  Agreements.  Except as set forth on Schedule 5.15 or as
disclosed  in the  Company's  proxy  statement  for its 1999  annual  meeting of
stockholders  or as filed on the  Company's  most recent  Annual  Report on Form
10-K,  the  Company is not party to nor bound by any  agreement  or  commitment,
written or oral, which obligates the Company to make payments to any person,  or
which obligates any person to make payments to the Company,  in the case of each
such agreement in an amount exceeding $60,000, or which is otherwise material to
the  conduct  and  operation  of  the  business  of  the  Company  or any of its

                                       8
<PAGE>

properties  or  assets,   including,   without   limitation,   all  shareholder,
employment, non-competition and consulting agreements and employee benefit plans
and arrangements and collective  bargaining agreements to which the Company is a
party  or by  which  it  is  bound.  The  Company  has  performed  all  material
obligations required to be performed by it, and is not in default, or in receipt
of any claim,  under any such  agreement or  commitment,  and the Company has no
present   expectation  or  intention  of  not  fully   performing  all  of  such
obligations,  nor  does  the  Company  have  any  knowledge  of  any  breach  or
anticipated  breach by the other  parties to any such  agreement or  commitment.
Each  Purchaser has been  furnished  with, or the Company has made available for
such  Purchaser's  review,  a true and correct  copy of each  written  agreement
referred to in Schedule  5.15,  together with all  amendments,  waivers or other
changes thereto.

                  5.16. Undisclosed Liabilities. Except to the extent reflected,
disclosed or reserved  against in the Financial  Statements or the notes thereto
and except for  liabilities  incurred  since  September 30, 1999 in the ordinary
course  and  consistent  with  past  practice,  the  Company  does  not have any
obligation  or liability  whether  absolute,  accrued,  contingent or otherwise,
which is material to the business,  operations, assets or financial condition of
the Company.

                  5.17. Employees;  Conflicting Agreements.  (a) The Company has
caused all present members of management and all  professional  employees of and
consultants and advisors to the Company, including all employees and consultants
and  advisors  involved in  research  and  development,  and will cause all such
persons  in  the  future,  to be  subject  to  agreements  with  respect  to (i)
nondisclosure   of  confidential   information,   (ii)  assignment  of  patents,
trademarks,   copyrights  and  proprietary  rights  to  the  Company  and  (iii)
disclosure to the Company of inventions.

                  (b) To the best knowledge of the Company after due inquiry, no
stockholder,  director,  officer or key employee of the Company is a party to or
bound by any agreement,  contract or commitment,  or subject to any restrictions
in connection with any previous or current  employment of any such person (other
than as set forth on  Schedule  5.17(b)  with  respect  to the  Company),  which
materially  adversely affects,  or which in the future may materially  adversely
affect,  the business or the  proposed  business of the Company or the rights of
any of the Purchasers under this Agreement.

                  5.18.  Disclosure.  Neither  this  Agreement  nor  any  of the
schedules,  exhibits, written statements,  documents or certificates prepared or
supplied by the Company with respect to the  transactions  contemplated  by this
Agreement  contain any untrue  statement  of a material  fact or omit a material
fact necessary to make the statements  contained therein not misleading in light
of the  circumstances  under which made.  Except for  general  factors  that are
common in the market and industry of the Company and such other information made
available to the Purchasers and their  representatives,  there exists no fact or
circumstance  which,  to the best  knowledge  of the Company  after due inquiry,
materially adversely affects, or which could reasonably be anticipated to have a
material  adverse  effect on, the  existing  or  expected  financial  condition,
operating results,  assets,  customer relations,  employee relations or business
prospects of the Company.

                                       9
<PAGE>

                  5.19.  Compliance  with  Securities  Laws.  (a)  Assuming  the
accuracy and truth of each of Purchasers'  representations  set forth in Section
6, all  securities  of the  Company  heretofore  sold and  issued  were sold and
issued,  and the Common  Shares were  offered  and will be sold and  issued,  in
compliance  with all  applicable  federal,  state and foreign  securities  laws.
Neither the Company, nor any of its Affiliates, nor, to its best knowledge after
due inquiry, any person or entity acting on its or their behalf has, directly or
indirectly,  made any offers or sales of any security or solicited any offers to
buy any security,  under  circumstances  that would require  registration of the
Common  Shares under the  Securities  Act of 1933,  as amended (the  "Securities
Act") or for the offering of the same to be integrated  with any other  offering
of securities.

                  (b) The Company has not  directly or  indirectly  purchased or
redeemed  any shares of Common Stock  during the 30 days  preceding  the Closing
Date.

                  5.20.  Brokers.  Except  as set  forth on  Schedule  5.20,  no
finder,  broker,  agent,  financial  person or other  intermediary  has acted on
behalf of the Company in connection with the offering of the Common Shares,  the
execution  of the  Agreement  or  the  consummation  of any of the  transactions
contemplated hereby.

                  5.21.  Transactions  with  Affiliates.  Except as set forth on
Schedule 5.21 or in the Company's proxy statement for its 1999 annual meeting of
stockholders,  no  director,  officer,  employee,  consultant  or  agent  of the
Company,  or  member  of the  family  of any  such  person  or any  corporation,
partnership,  trust or other entity in which any such  person,  or any member of
the family of any such person,  has a substantial  interest in or is an officer,
director,  trustee, partner or holder of more than 5% of the outstanding capital
stock thereof,  is a party to any  transaction  with the Company,  including any
contract,  agreement  or other  arrangement  providing  for the  employment  of,
furnishing of services by or requiring payments to any such person or firm.

                  5.22.   Environmental   Matters.  (a)  The  Company,  and  all
properties owned, operated or leased by the Company, have obtained and currently
maintain  all material  environmental  permits  required for their  business and
operations and are in compliance with all such environmental  permits. There are
no legal proceedings pending nor, to the best knowledge of the Company after due
inquiry,  threatened  to modify or revoke any such  environmental  permits.  The
Company  has not  received  any notice from any source that there is lacking any
environmental  permit  required for the current use or operation of the business
of the Company, or any property owned, operated or leased by the Company.

                  (b) Except as set forth on Schedule  5.22,  all real  property
owned,  operated or leased by the  Company,  and, to the best  knowledge  of the
Company after due inquiry,  all property  adjacent to such properties,  are free
from  contamination by any hazardous  material other than any such contamination
as would not have a Material  Adverse Effect;  and the Company is not subject to
environmental costs and liabilities with respect to hazardous materials,  and no
facts or circumstances  exist which could give rise to  environmental  costs and
liabilities with respect to hazardous materials.

                                       10
<PAGE>

                  (c) Except as set forth on  Schedule  5.22,  there is not now,
nor, to the best  knowledge of the Company after due inquiry,  has there been in
the past, on, in, or under any real property owned,  leased,  or operated by the
Company, or by any of their respective  predecessors (i) any asbestos-containing
materials, (ii) any underground storage tanks, (iii) above-ground storage tanks,
(iv)   impoundments,   (v)   poly-chlorinated   biphenyls  or  (vi)  radioactive
substances.

                  (d) The Company, and all properties owned,  operated or leased
by the Company, comply with all environmental laws.

                  (e) Since June 30, 1998, neither the Company, nor any property
owned,  leased or  operated  by the  Company,  has  received  or been issued any
written request for  information,  or has been notified that it is a potentially
responsible  party under the  environmental  laws with respect to any on-site or
off-site for which environmental costs and liabilities are asserted.

                  6.  Representations,  Warranties  and Covenants of Purchasers.
Purchasers  severally  represent,  warrant and covenant to the Company as of the
Closing Date as follows:

                   6.1.  Investment  Intent.  Each  Purchaser is an  "accredited
investor"  within the meaning of  Regulation D under the  Securities  Act.  Each
Purchaser  has   experience  in  making   investments   in   development   stage
biotechnology  companies  and is acquiring the Common Shares for its own account
and not with a present view to, or for sale in connection with, any distribution
thereof in violation of the  registration  requirements  of the Securities  Act.
Each  Purchaser  consents  to  the  placing  of a  legend  on  the  certificates
representing its respective Common Shares to the effect that, and each Purchaser
acknowledges  that,  such  Common  Shares  have not been  registered  under  the
Securities Act and may not be transferred  unless  registered in accordance with
applicable securities laws or, in the opinion of counsel to the Purchasers (such
opinion to be in form and  substance  reasonably  satisfactory  to the Company),
exempt therefrom.

                  6.2. Authorization. Each Purchaser has the power and authority
to execute and deliver this Agreement and to perform its obligations  hereunder,
having obtained all required consents, if any, and this Agreement, when executed
and  delivered,  will  constitute a legal valid and binding  obligation  of such
Purchaser  except  as such  enforceability  may be  limited  by (a)  bankruptcy,
insolvency,  moratorium and similar laws affecting  creditors'  rights generally
and (b) the availability of remedies under general equitable principles.

                  6.3. Brokers. No finder,  broker,  agent,  financial person or
other  intermediary has acted on behalf of the Purchasers in connection with the
offering of the Common Shares or the  consummation  of this  Agreement or any of
the transactions contemplated hereby.

                  6.4.  No Short.  For a period of six months  from the  Closing
Date, the Purchasers will not "short" or "short against the box" (as those terms
are generally understood) any equity security of the Company; provided, however,
that if the Shelf Registration  Statement (as defined below) is not effective by
the date that is 60 days following the Closing Date,  then the Purchasers  shall
have no  obligation  under  this  section  6.4  until  such  time  as the  Shelf
Registration Statement is declared effective by the SEC.

                                       11
<PAGE>

                  7. Covenants of the Company. Until such time as (a) Purchasers
and their Affiliates  beneficially own less than five percent (5%) of the Common
Stock then  outstanding,  the Company  covenants  and agrees with  Purchasers as
follows:

                  7.1.  Books and Accounts.  The Company will: (a) make and keep
books, records and accounts,  which, in reasonable detail, accurately and fairly
reflect its  transactions,  including  without  limitation,  dispositions of its
assets;  and (b) devise and  maintain a system of internal  accounting  controls
sufficient to provide  reasonable  assurances that (i) transactions are executed
in  accordance  with  management's  general  or  specific  authorization,   (ii)
transactions  are  recorded as  necessary  to permit  preparation  of  financial
statements in conformity with generally  accepted  accounting  principles and in
accordance with the Company's past practices or any other criteria applicable to
such  statements,  and to maintain  accountability  for assets,  (iii) access to
assets is permitted  only in accordance  with  management's  general or specific
authorization,  and (iv) the recorded accountability for assets is compared with
the existing assets at reasonable intervals and appropriate action is taken with
respect to any differences.

                  7.2.  Periodic  Reports.  The  Company  will  furnish  to  the
Purchasers, other than documents available via EDGAR: (i) as soon as practicable
(but in the case of the annual report of the Company to its stockholders, within
ninety (90) days after the end of each fiscal year of the  Company) one copy of:
(A) its annual  report to its  stockholders  (which  annual report shall contain
financial  statements audited in accordance with generally  accepted  accounting
principles  in the  United  States  of  America  by a firm of  certified  public
accountants  of  recognized  standing),  (B) if not included in substance in its
annual report to  stockholders,  its annual report on Form 10-K, (C) each of its
quarterly reports to its  stockholders,  and if not included in substance in its
quarterly  reports to stockholders,  its quarterly report on Form 10-Q, (D) each
of its  current  reports  on  Form  8-K,  and  (E) a  copy  of  the  full  Shelf
Registration  Statement  (as  defined  below),  (the  foregoing,  in each  case,
excluding exhibits);  and (ii) upon reasonable request, all exhibits excluded by
the parenthetical to the immediately preceding clause 7.2(a)(i)(E) and any other
information published by the Company that is generally available to the public.

                  7.3. Other Reports and Inspection. The Company will furnish to
the  Purchasers,  other  than  documents  available  via  EDGAR:  (a) as soon as
practicable  after  issuance,  copies of any  financial  statements  or  reports
prepared by the Company for, or otherwise  furnished to, its stockholders or the
SEC  (other  than  information  furnished  to  the  SEC  on  a  confidential  or
supplemental  basis)  and  (b)  promptly,  such  other  documents,  reports  and
financial  data  as  Purchasers  may  reasonably  request,   provided  that  the
Purchasers  agree to preserve  the  confidential  nature of, and to refrain from
trading on the basis of, material  requested by the Purchasers which the Company
has marked as confidential.  In addition the Company will, upon reasonable prior
notice, make available to Purchasers or its representatives or designees (x) all
assets,  properties  and  non-confidential  business  records of the Company for
inspection  and (y) the  directors  and  officers of the Company for  interviews
concerning the business, affairs and finances of the Company.

                                       12
<PAGE>

                  7.4.  Insurance.  The Company will at all times maintain valid
policies  of  worker's  compensation  insurance  and such other  insurance  with
respect to its properties and business of the kinds and in amounts not less than
is  customarily  maintained  by  corporations  engaged  in the  same or  similar
business  and  similarly  situated,  including,  without  limitation,  insurance
against  fire,  loss,  damage,  theft,  public  liability  and other risks.  The
activities  and  operations  of the Company  shall be  conducted  in a manner to
conform in all material respects to all applicable provisions of such policies.

                  7.5. Use of Proceeds.  The Company  shall use the net proceeds
from the sale of the Common Shares for the redemption of all outstanding  shares
of its  Series F  Convertible  Preferred  Stock at a price  equal to 109% of the
stated value of such Series F  Convertible  Preferred  Stock (which is $10,000).
Any  net  proceeds  exceeding  the  amount  required  to  redeem  the  Series  F
Convertible Preferred Stock shall be used for general corporate purposes.

                  7.6.  Transactions with Affiliates.  Except for employment and
consulting agreements entered into in the ordinary course of business (including
such  agreements  in  effect  as of  the  Closing  Date)  and  the  transactions
contemplated  by  this  Agreement,  the  Company  shall  not (a)  engage  in any
transaction  with,  (b) make any loans  to,  nor (c)  enter  into any  contract,
agreement or other  arrangement (i) providing for (x) the employment of, (y) the
furnishing of services by (other than  employment and consulting  services),  or
(z) the rental of real or personal  property from, or (ii)  otherwise  requiring
payments  to,  any  officer,  director  or key  employee  of the  Company or any
relative of such persons or any other "associate" of such persons (as such terms
are defined in the rules and regulations  promulgated under the Securities Act),
without the prior written  approval of the Purchasers,  which approval shall not
be unreasonably withheld.

                  7.7. Corporate Existence, Licenses and Permits; Maintenance of
Properties;  New Businesses.  The Company will at all times conduct its business
in the  ordinary  course  and will use its best  efforts to cause to be done all
things necessary to maintain,  preserve and renew its existence and will use its
best efforts to preserve and keep in force and effect, all licenses, permits and
authorizations  necessary to the conduct of its business.  The Company will also
maintain and keep its  properties in good repair,  working order and  condition,
and from time to time,  to make all needful  and proper  repairs,  renewals  and
replacements,  so that the business  carried on in  connection  therewith may be
properly conducted at all times.

                  7.8. Other Material Obligations. The Company will use its best
efforts to comply in all material  respects with,  (a) all material  obligations
which it is subject  to, or becomes  subject  to,  pursuant  to any  contract or
agreement,  whether  oral or written,  as such  obligations  are  required to be
observed  or  performed,  unless  and to the  extent  that the  same  are  being
contested in good faith and by appropriate  proceedings  and the Company has set
aside  on its  books  adequate  reserves  with  respect  thereto,  and  (b)  all
applicable laws,  rules, and regulations of all  governmental  authorities,  the
violation  of which  could have a material  adverse  effect  upon the  business,
financial  condition,  operating  results,  employee  or customer  relations  or
prospects of the Company.

                                       13
<PAGE>

                  7.9.  Amendment to the  Certificate of  Incorporation  and the
By-Laws.  The Company will perform and be in compliance  with and observe all of
the provisions set forth in its Certificate of Incorporation  and By-Laws to the
extent that the performance of such obligations is legally permissible; provided
that the fact that performance is not legally  permissible will not prevent such
nonperformance  from  constituting  an event of default  under  this  Agreement.
Except  with  the  consent  of  the  Purchasers,  which  consent  shall  not  be
unreasonably   withheld,   the  Company  will  not  amend  its   Certificate  of
Incorporation  or By-Laws or any Certificate of  Designations  for any series of
Preferred  Stock  of  the  Company  so as to  affect  adversely  the  rights  of
Purchasers  under  this  Agreement,  the  Certificate  of  Incorporation  or the
By-Laws.

                  7.10.  Consents  and  Waivers.  The Company has  obtained  all
consents and waivers needed to enable it to perform all of its obligations under
this Agreement and the transactions contemplated hereby.

                  7.11.  Taxes  and  Liens.  The  Company  shall  duly  pay  and
discharge when payable, all taxes,  assessments and governmental charges imposed
upon or against the Company or its  properties,  or any part thereof or upon the
income or profits therefrom,  in each case before the same become delinquent and
before penalties accrue thereon,  as well as all claims for labor,  materials or
supplies  which if unpaid  might by law become a lien upon any of its  property,
unless and to the extent that the same are being  contested in good faith and by
appropriate  proceedings  and the  Company  has set aside on its books  adequate
reserves with respect thereto.

                  7.12. Restrictive Agreement.  The Company covenants and agrees
that  subsequent  to the  Closing,  it shall not be a party to any  agreement or
instrument  which by its terms would  restrict the Company's  performance of its
obligations  pursuant to this  Agreement,  the Certificate of  Incorporation  or
By-laws of the Company or the Common Shares.

                  7.13. Publicity. The Company shall not issue any press release
or make any other  public  announcement  with  respect to this  Agreement or the
transactions  contemplated  hereby or utilizing the names of Purchasers or their
officers, directors, employees, agents or Affiliates without obtaining the prior
approval of Purchasers,  except as may be required by law or the  regulations of
any securities exchange.

                  7.14.  Restriction  on  Securities.  (a) During  the  12-month
period  following the Closing Date,  the Company will not extend the  expiration
date or lower the exercise price of any options or warrants, or take any similar
action with respect to any convertible securities of the Company.

                  (b) Prior to the Closing  Date,  the Company  shall obtain the
written agreement of all executive  officers and directors of the Company to (i)
"lock-up"  all of the shares of Common  Stock  owned by each of them at any time
until  (1)  the  date on  which  all  Common  Shares  may be  sold  in a  single
transaction  on a  registered  securities  exchange or national  market under an
applicable  exemption from the  registration  requirements of the Securities Act
and all other  applicable  securities  laws and (2) the date that is six  months

                                       14
<PAGE>

following the Closing Date;  provided that the executive  officers and directors
of the Company may sell an aggregate of one million (1,000,000) shares of Common
Stock in such 6-month period so long as any such  executive  officer or director
provide to the Purchasers a written notice of their intent to sell at least five
(5) days prior to the earlier of (A) the filing of a Form 144 by such person and
(B) the date of such proposed sale, (ii) not directly or indirectly sell "short"
or "short against the box" (as those terms are generally understood),  until the
date that is 6 months following the Closing Date.

                  7.15.  Restriction  on Liens.  The Company shall not create or
permit  the  imposition  of any  liens on any of its  assets  from and after the
Closing Date without the prior written authorization of the Board of Directors.

                  7.16. Restrictions on Indebtedness. Without the prior approval
of the Board of Directors, the Company shall not incur, create, assume or permit
to exist any indebtedness except (i) pursuant to equipment lease financings with
commercial  banks or Persons  whose  business  consists in  substantial  part of
engaging in such financings,  (ii) pursuant to customary accounts receivable and
inventory financing in the ordinary course of business,  (iii) in an amount less
than $100,000 incurred in the ordinary course of business, and (iv) indebtedness
for borrowed  money  existing on the date hereof and disclosed in writing to the
Purchasers,   but  not  any   extensions,   renewals  or  replacements  of  such
indebtedness.

                  7.17.  Board of Directors.  (a) The Company shall at all times
maintain   provisions  in  its  By-laws  and/or   Certificate  of  Incorporation
indemnifying  all directors  against  liability and absolving all directors from
liability to the Company and its  stockholders  to the maximum extent  permitted
under the laws of the State of Delaware.

                  (b) The By-laws of the Company shall always contain provisions
consistent  with the  provisions  of this Section 7.17 except to the extent this
Section 7.17 deals with the possible observer.

                  7.18.   Certain   Subsidiaries.   Except  for   wholly   owned
subsidiaries of the Company.,  the Company will not create any entity that would
be a Subsidiary (as defined in Section 9.9) without the prior written consent of
the  Purchasers.  Notwithstanding  the  foregoing,  the  Company may acquire any
interest in any business from any person,  firm or entity (whether by a purchase
of assets,  purchase of stock,  merger or otherwise) using cash or stock without
the prior written consent of the Purchasers.

                  7.19.  Listing.  The  Company  will take all action  necessary
promptly to file an  Application  for Listing of  Additional  Shares with Nasdaq
National  Market  and/or  take any other  necessary  action to enable the Common
Stock to trade on a national market.

                  7.20.  Material Changes.  The Company will promptly notify the
Purchasers  of  any  material  adverse  change  in  its  business  or  financial
condition.

                  7.21.  Adjustment  to Per Share Price.  If,  commencing on the
date that is six months from the Closing Date and ending on the date that is one
year from the  Closing  Date,  the Company  issues  shares of Common  Stock,  or
securities  convertible  into or  exercisable  for shares of Common Stock,  at a

                                       15
<PAGE>

price  per  share  less  than  the Per  Share  Price,  then  the  Company  shall
simultaneously issue to the Purchasers for no additional consideration, a number
of shares of Common  Stock  sufficient  to reduce  the Per Share  Price  then in
effect to equal the "Adjusted  Price" (as defined  below).  For purposes of this
section  7.21(b),  the term Adjusted  Price (which shall not be greater than the
Per Share Price then in effect)  shall equal a fraction,  the numerator of which
shall equal (1) the sum of (A) the number of shares of Common Stock  outstanding
on the record date of such  issuance or sale  multiplied  by the Per Share Price
then in effect  plus (B) the Total  Consideration  (as defined  below),  and the
denominator  of which shall be the number of shares of Common Stock  outstanding
on the  record  date of such  issuance  or  sale  plus  the  maximum  number  of
additional  shares of Common Stock  issued,  sold or issuable  upon  exercise or
conversion  of such  securities.  "Total  Consideration"  shall  mean the  total
amount,  if any,  received or receivable by the Company in  consideration of the
issuance  or sale of such  securities  plus  the  total  consideration,  if any,
payable to the Company upon  exercise  thereof.  The  provisions of this section
7.21(b)  shall  not  apply  (i) to  issuances  of  securities  in any  corporate
partnering  arrangements (including mergers) consummated by the Company, (ii) to
the exercise or conversion of options,  warrants or other convertible securities
outstanding  as of the  Closing  Date,  or  (iii)  to  issuances  which,  in the
aggregate, yield gross proceeds to the Company of less than $250,000.

                  7.22. Right of First Refusal. In the event that, within the 12
month  period  following  the Closing  Date,  the  Company  intends to conduct a
private placement of its securities through a placement agent,  broker-dealer or
finder, pursuant to which it will pay such agent a commission,  then the Company
shall (a) notify Paramount Capital, Inc. ("Paramount") of such intent in writing
detailing the terms of such proposed  offering and (b) grant Paramount the right
of first  refusal to act as  placement  agent for the  Company  in such  private
placement.  Paramount shall notify the Company within 15 days of its intent.  In
the event that Paramount  declines to act as placement  agent for the Company on
the terms  proposed  to  Paramount  in the notice and the  Company  subsequently
offers to a third-party  the opportunity to act as placement agent on terms more
favorable  than those  offered to  Paramount,  then the Company must first offer
such opportunity to Paramount on such more favorable terms.

         8.       Registration of Common Stock.

         8.1.  Registration.  (i) Not later than 30 days after the Closing Date,
the Company will file with the SEC a shelf  registration  statement  (the "Shelf
Registration  Statement")  with  respect  to the  resale  of the  Common  Shares
beneficially  owned  by  Purchasers  following  the  Closing  (the  "Registrable
Securities"). The Company will use its best efforts to effect the registrations,
qualifications or compliances (including,  without limitation,  the execution of
any  required  undertaking  to  file  post-effective   amendments,   appropriate
qualifications  under  applicable  blue sky or other state  securities  laws and
appropriate   compliance  with  applicable  securities  laws,   requirements  or
regulations)  as may be  reasonably  requested and as would permit or facilitate
that sale and distribution of all Registrable  Securities until the distribution
thereof  is  complete;  provided  that the  Company  shall not be  obligated  to
maintain the effectiveness of the Shelf Registration  Statement (and any related
qualifications and compliance)  following such time as the Company shall deliver
an opinion of counsel  reasonably  satisfactory  to the  holders of  Registrable
Securities (the "Holders') and in form and substance satisfactory to each Holder

                                       16
<PAGE>

that  (i)  such  Holders  may  sell  in a  single  transaction  all  Registrable
Securities  then held or  issuable  to such  Holder on a  registered  securities
exchange or Nasdaq market under an applicable  exemption  from the  registration
requirements of the Securities Act and all other applicable  securities laws and
(ii) all  transfer  restrictions  and  restrictive  legends with respect to such
Registrable Securities will be removed upon the consummation of such sale.

                  8.2.   Registration   Procedures.   In  connection   with  the
registration of any Registrable  Securities under the Securities Act as provided
in this Section 8, the Company will use its best efforts,  as  expeditiously  as
possible to:

                  (a)  Prepare  and  file  with the SEC the  Shelf  Registration
Statement with respect to such  Registrable  Securities and use its best efforts
to cause such Shelf Registration  Statement to become effective as expeditiously
as possible;

                  (b)  Prepare  and  file  with  the  SEC  such  amendments  and
supplements  to such Shelf  Registration  Statement and the  prospectus  used in
connection  therewith  as may be  necessary  to  keep  such  Shelf  Registration
Statement  effective  until the disposition of all securities in accordance with
the intended  methods of disposition by the seller or sellers  thereof set forth
in such Shelf Registration Statement shall be completed,  and to comply with the
provisions of the Securities Act (to the extent  applicable to the Company) with
respect to such dispositions;

                  (c) Furnish to each seller of such Registrable Securities such
number of copies of such Shelf Registration Statement and of each such amendment
and supplement  thereto (in each case  including all  exhibits),  such number of
copies  of  the  prospectus  included  in  such  Shelf  Registration   Statement
(including each preliminary prospectus),  in conformity with the requirements of
the  Securities  Act, and such other  documents,  as such seller may  reasonably
request,  in order to facilitate the disposition of the  Registrable  Securities
owned by such seller;

                  (d)  Use  its  best   efforts  to  register  or  qualify  such
Registrable  Securities covered by such Shelf Registration  Statement under such
other securities or blue sky laws of such jurisdictions as any seller reasonably
requests,  and do any and all other  acts and  things  which  may be  reasonably
necessary or advisable to enable such seller to consummate  the  disposition  in
such  jurisdictions of the Registrable  Securities owned by such seller,  except
that the Company will not for any such purpose be required to qualify  generally
to do business as a foreign  corporation  in any  jurisdiction  wherein it would
not,  but for the  requirements  of  this  Section  8.2(d)  be  obligated  to be
qualified, to subject itself to taxation in any such jurisdiction, or to consent
to general service of process in any such jurisdiction;

                  (e)  Provide  a  transfer  agent  and  registrar  for all such
Registrable  Securities covered by such Shelf  Registration  Statement not later
than the effective date of such Shelf Registration Statement;

                  (f) Notify each seller of such  Registrable  Securities at any
time when a prospectus  relating  thereto is required to be delivered  under the
Securities  Act,  of the  happening  of any  event  as a  result  of  which  the
prospectus  included  in such Shelf  Registration  Statement  contains an untrue

                                       17
<PAGE>
statement of a material fact or omits any fact  necessary to make the statements
therein not misleading, and, at the request of any such seller, the Company will
prepare a supplement  or amendment to such  prospectus  so that,  as  thereafter
delivered to the purchasers of such Registrable Securities, such prospectus will
not  contain an untrue  statement  of a material  fact or omit to state any fact
necessary to make the statements therein not misleading. The Purchasers agree to
suspend, upon request of the Company, any disposition of Registrable  Securities
pursuant to the Registration  Statement  contemplated  hereby during any period,
not to exceed one 30-day period per circumstance or development.

                  (g) Cause all such Registrable Securities to be listed on each
securities  exchange  or  automated  over-the-counter  trading  system  on which
similar securities issued by the Company are then listed;

                  (h) Enter into such customary  agreements  (including,  in the
event  Purchasers  elect to engage an underwriter  in connection  with the Shelf
Registration Statement, an underwriting agreement containing customary terms and
conditions)  and take all such other actions as reasonably  required in order to
expedite or facilitate the disposition of such Registrable Securities; and

                  (i) Make available for inspection by any seller of Registrable
Securities, all financial and other records, pertinent corporation documents and
properties  of the Company,  and cause the  Company's  officers,  directors  and
employees to supply all information  reasonably  requested by any such seller in
connection with the Shelf Registration Statement pursuant to Section 8.1.

                  8.3  Registration  and  Selling  Expenses.  (a)  All  expenses
incurred by the  Company in  connection  with the  Company's  performance  of or
compliance  with  this  Section  8,  including,   without   limitation  (i)  all
registration and filing fees (including all expenses incident to filing with the
National  Association  of  Securities  Dealers,  Inc.),  (ii)  blue sky fees and
expenses,  (iii) all necessary printing and duplicating expenses,  (iv) all fees
and disbursements of counsel and accountants  retained by the Company (including
the  expenses of any audit of  financial  statements)  and (v) a single  counsel
retained by the  Purchasers;  provided that the Company shall not be required to
pay for the costs of any in-house counsel and the amount of any fees for outside
counsel  shall be offset  against the $10,000 cap described in Section 11.2 (all
such expenses being called "Registration Expenses"), will be paid by the Company
except as otherwise expressly provided in this Section 8.3.

                  (b) The Company  will, in any event,  in  connection  with any
registration   statement,   pay  its  internal  expenses   (including,   without
limitation,  all salaries and expenses of its officers and employees  performing
legal, accounting or other duties in connection therewith and expenses of audits
of year-end financial  statements),  the expense of liability  insurance and the
expenses and fees for listing the  securities  to be  registered  on one or more
securities  exchanges or  automated  over-the-counter  trading  systems on which
similar securities issued by the Company are then listed.

                                       18
<PAGE>

                  (c) Nothing in this  Agreement  shall be  construed to prevent
any Holder or Holders of Registrable  Securities  from retaining such counsel as
they shall choose at their own expense.

                  8.4. Other Public Sales and Registrations.  The Company agrees
that it will not, on its own behalf, file or cause to become effective any other
registration  of any of its  securities  under the  Securities  Act or otherwise
effect a public  sale or  distribution  of its  securities  (except  pursuant to
registration  on Form S-8 and  Form  S-4 or any  successor  form  relating  to a
special  offering to the employees or security  holders of the Company) until at
least 60 days have elapsed  after the effective  date of the Shelf  Registration
Statement without the prior written consent of the Purchasers.

                  8.5. Indemnification.  (a) The Company shall indemnify, to the
extent permitted by law, each holder of Registrable Securities, its officers and
directors,  if any, and each person, if any, who controls such holder within the
meaning of the Securities Act, against all losses, claims, damages,  liabilities
and expenses (under the Securities Act or common law or otherwise) caused by any
untrue statement or alleged untrue statement of a material fact contained in any
registration  statement or  prospectus  (and as amended or  supplemented  if the
Company has furnished any amendments or supplements  thereto) or any preliminary
prospectus,  which registration statement,  prospectus or preliminary prospectus
shall be prepared  in  connection  with the  registration  contemplated  by this
Section 8, or caused by any  omission  or alleged  omission  to state  therein a
material fact required to be stated  therein or necessary to make the statements
therein  not  misleading,  except  insofar  as  such  losses,  claims,  damages,
liabilities  or expenses are caused by any untrue  statement  or alleged  untrue
statement  contained in or by any omission or alleged  omission from information
furnished  in  writing by such  holder to the  Company  in  connection  with the
registration  contemplated  by this Section 8,  provided the Company will not be
liable pursuant to this Section 8.5 if such losses, claims, damages, liabilities
or expenses have been caused by any selling security holder's failure to deliver
a copy  of the  registration  statement  or  prospectus,  or any  amendments  or
supplements thereto, after the Company has furnished such holder with the number
of copies required by Section 8.2(c).

                  (b) In connection with any  registration  statement in which a
holder of  Registrable  Securities  is  participating,  each such  holder  shall
furnish to the Company in writing such information as is reasonably requested by
the Company for use in any such  registration  statement or prospectus and shall
severally,  but not  jointly,  indemnify,  to the extent  permitted  by law, the
Company,  its directors  and officers and each person,  if any, who controls the
Company within the meaning of the Securities  Act,  against any losses,  claims,
damages, liabilities and expenses resulting from any untrue statement or alleged
untrue  statement of a material  fact or any  omission or alleged  omission of a
material fact required to be stated in the registration  statement or prospectus
or any  amendment  thereof  or  supplement  thereto  or  necessary  to make  the
statements therein not misleading,  but only to the extent such losses,  claims,
damages,  liabilities  or expenses are caused by an untrue  statement or alleged

                                       19
<PAGE>
untrue  statement  contained  in or by an  omission  or  alleged  omission  from
information  so  furnished  in writing  by such  holder in  connection  with the
registration  contemplated  by this Section 8. If the  offering  pursuant to any
such registration is made through underwriters, each such holder agrees to enter
into an underwriting  agreement in customary form with such  underwriters and to
indemnify such  underwriters,  their  officers and  directors,  if any, and each
person who controls such  underwriters  within the meaning of the Securities Act
to the same extent as hereinabove  provided with respect to  indemnification  by
such holder of the Company. Notwithstanding the foregoing or any other provision
of this  Agreement,  in no event  shall a holder of  Registrable  Securities  be
liable for any such losses, claims,  damages,  liabilities or expenses in excess
of the lesser of (a) the net proceeds received by such holder in the offering or
(b) $500,000.

                  (c)  Promptly  after  receipt by an  indemnified  party  under
Section  8.5  (a)  or (b)  of  notice  of the  commencement  of  any  action  or
proceeding,  such indemnified  party will, if a claim in respect thereof is made
against the indemnifying party under such Section, notify the indemnifying party
in  writing  of the  commencement  thereof;  but the  omission  so to notify the
indemnifying  party will not relieve it from any liability  which it may have to
any indemnified party otherwise than under such Section. In case any such action
or  proceeding is brought  against any  indemnified  party,  and it notifies the
indemnifying party of the commencement  thereof,  the indemnifying party will be
entitled to participate therein, and, to the extent that it wishes, jointly with
any other indemnifying party similarly notified,  to assume the defense thereof,
with  counsel  approved  by such  indemnified  party  (such  approval  not to be
unreasonably  withheld),  and after notice from the  indemnifying  party to such
indemnified  party  of its  election  so to  assume  the  defense  thereof,  the
indemnifying  party  will not be liable to such  indemnified  party  under  such
Section  for any  legal or any  other  expenses  subsequently  incurred  by such
indemnified  party in connection with the defense thereof (other than reasonable
costs  of  investigation)   unless  incurred  at  the  written  request  of  the
indemnifying  party.  Notwithstanding the above, the indemnified party will have
the right to employ  counsel of its own choice in any such action or  proceeding
if the  indemnified  party has  reasonably  concluded that there may be defenses
available  to it  which  are  different  from  or  additional  to  those  of the
indemnifying  party, or counsel to the indemnified  party is of the opinion that
it  would  not  be  desirable  for  the  same  counsel  to  represent  both  the
indemnifying party and the indemnified party because such  representation  might
result in a conflict  of  interest  (in either of which  cases the  indemnifying
party  will not have the  right to  assume  the  defense  of any such  action or
proceeding  on behalf of the  indemnified  party or  parties  and such legal and
other expenses will be borne by the indemnifying  party). An indemnifying  party
will not be  liable to any  indemnified  party  for any  settlement  of any such
action or proceeding effected without the consent of such indemnifying party.

                  (d) If the  indemnification  provided for in Section 8.5(a) or
(b) is unavailable  under  applicable law to an indemnified  party in respect of
any losses,  claims,  damages or  liabilities  referred  to  therein,  then each
applicable  indemnifying  party, in lieu of indemnifying such indemnified party,
shall  contribute to the amount paid or payable by such  indemnified  party as a
result of such losses,  claims,  damages or liabilities in such proportion as is
appropriate  to reflect the relative fault of the Company on the one hand and of
the Holders on the other in connection  with the  statements or omissions  which
resulted in such losses, claims,  damages, or liabilities,  as well as any other
relevant equitable considerations.  The relative fault of the Company on the one
hand and of the Holders on the other shall be  determined by reference to, among
other things,  whether the untrue or alleged untrue statement of a material fact
or the omission to state a material fact relates to information  supplied by the
Company or by the Holders and the parties' relative intent, knowledge, access to
information  and  opportunity  to correct or prevent such statement or omission.
The amount paid or payable by a party as a result of the losses, claims, damages
and  liabilities  referred to above  shall be deemed to include,  subject to the

                                       20
<PAGE>

limitations  set forth in Section  8.5(c),  any legal or other fees or  expenses
reasonably  incurred by such party in connection with investigating or defending
any action or claim.  No person guilty of fraudulent  misrepresentation  (within
the  meaning  of  Section  11(f) of the  Securities  Act)  will be  entitled  to
contribution   from  any   person   who  is  not   guilty  of  such   fraudulent
misrepresentation.

                  (e)  Promptly  after  receipt by the  Company or any holder of
Securities of notice of the commencement of any action or proceeding, such party
will,  if a claim for  contribution  in respect  thereof  is to be made  against
another party (the "contributing  party"),  notify the contributing party of the
commencement  thereof; but the omission so to notify the contributing party will
not  relieve it from any  liability  which it may have to any other  party other
than for contribution  under this Agreement.  In case any such action,  suit, or
proceeding is brought against any party,  and such party notifies a contributing
party of the commencement  thereof,  the contributing  party will be entitled to
participate  therein with the notifying party and any other  contributing  party
similarly notified.

                  8.6.   Additional   Common  Stock   Issuable   Upon  Delay  of
Registration and Other Events.  (a) Except to the extent any delay is due to the
failure of a Holder to  reasonably  cooperate  in  providing to the Company such
information  as shall be reasonably  requested by the Company in writing for use
in the Shelf Registration  Statement, if the Shelf Registration Statement is not
filed with the SEC  within 30 days  following  the  Closing  Date (the  "Outside
Target  Date"),  the Company  shall  immediately  declare,  issue and pay for no
additional  consideration to each Holder  additional  Common Shares equal to one
percent  (1%) of the Common  Shares  then held by such  Holder,  for each 15-day
period (or fraction thereof) after the Outside Target Date that the Registration
Statement remains unfiled.

                  (b) All  shares  of Common  Stock  issuable  pursuant  to this
Section 8.6 shall be duly  authorized,  fully paid and  nonassessable  shares of
Common  Stock  and  shall  be  included  in  the  Shelf  Registration  Statement
contemplated  by Section 8.1.  Such shares shall be  registered  in  Purchasers'
names or the name of the  nominee(s)  of  Purchasers  in such  denominations  as
Purchasers shall request pursuant to instructions delivered to the Company.

                  9. Certain  Definitions.  For the purposes of this  Agreement,
the following terms have the respective meanings set forth below:

                  9.1. "Affiliate" means any person, corporation, firm or entity
that  directly or  indirectly  controls,  is  controlled  by, or is under common
control with the indicated person, corporation, firm or entity.

                  9.2.     "Common Stock" means the Company's Common Stock.

                  9.3.    "Generally   Accepted  Accounting   Principles"  means
generally accepted accounting principles consistently applied.

                                       21
<PAGE>

                  9.4.   "Person"   shall  mean  any  natural   person  and  any
corporation,  partnership,  joint venture,  limited  liability  company or other
legal person, but shall not include any governmental entity.

                  9.5.     "Securities" means the Common Shares.

                  9.6.     "Securities  Act"  means,  as of any given time,  the
Securities Act of 1933, as amended, or any similar federal law then in force.

                  9.7.   "Exchange  Act"  means,  as  of  any  given  time,  the
Securities  Exchange Act of 1934, as amended, or any similar federal law then in
force.

                  9.8.  "SEC"  shall  mean  the  United  States  Securities  and
Exchange  Commission and includes any governmental  body or agency succeeding to
the functions thereof.

                  9.9.  "Subsidiary"  means  any  person,  corporation,  firm or
entity at least the majority of the equity  securities (or equivalent  interest)
of which are, at the time as of which any  determination is being made, owned of
record or  beneficially  by the  Company,  directly or  indirectly,  through any
Subsidiary or otherwise.

                  10.1  Indemnification.  (a) The Company  agrees to  indemnify,
defend and hold Purchasers and their officers,  directors,  partners,  employees
and consultants (the  "Purchasers'  Indemnitees")  harmless from and against any
direct damages or third-party  claims incurred or suffered by any of Purchasers'
Indemnitees as a result of or arising out of or in connection with the Company's
breach of any  representation,  warranty,  covenant or  agreement of the Company
contained in this Agreement. The Purchasers Indemnities will promptly notify the
Company  of any  potential  indemnification  claim upon  discovery  of the facts
supporting  the  potential  claim  and,  if such  indemnification  is based on a
third-party claim, allow the Company to defend, manage and resolve the matter at
the Company's cost and with the indemnities' reasonable cooperation.

                           (b) The  Purchasers  agree to  indemnify,  defend and
hold the  Company  and its  officers,  directors,  shareholders,  employees  and
consultants  (the  "Company  Indemnitees")  harmless from and against any direct
damages or third-party claims incurred or suffered by any of Company Indemnitees
as a result of or arising out of or in connection with the Purchasers' breach of
any representation,  warranty, covenant or agreement of the Purchasers contained
in this Agreement.  The Company  Indemnities will promptly notify the Purchasers
of any potential  indemnification  claim upon discovery of the facts  supporting
the  potential  claim and,  if such  indemnification  is based on a  third-party
claim,  allow the  Purchasers  to defend,  manage and  resolve the matter at the
Purchaser's cost and with the indemnities' reasonable cooperation.

                                       22
<PAGE>

                  11.      Miscellaneous.

                  11.1. Termination; Survival of Representations, Warranties and
Covenants.   Except  as   otherwise   provided   for  in  this   Agreement   all
representations,   warranties,   covenants  and  agreements  contained  in  this
Agreement,  or in any document,  exhibit,  schedule or  certificate by any party
delivered in  connection  herewith  shall  survive the execution and delivery of
this Agreement and the Closing Dates and the  consummation  of the  transactions
contemplated  hereby,  regardless of any investigation  made by Purchasers or on
their behalf.

                  11.2. Expenses.  The Company shall pay all its own expenses in
connection with this Agreement and the  transactions  contemplated  herein.  The
Company  agrees to pay  promptly  all  out-of-pocket  expenses  incurred  by the
Purchasers in connection with the preparation and  consummation of the Agreement
and the  transactions  contemplated  herein,  including but not limited to legal
fees  and  disbursements  of the  Purchasers'  counsel  in  connection  with the
preparation and consummation of this Agreement and the transactions contemplated
herein,   including   the  legal  fees  (other  than  legal  fees  for  in-house
counsel)_and  costs of negotiating and drafting any transaction  documents,  due
diligence and any necessary regulatory filings,  provided the total expenses for
which the Company is responsible shall be limited to $10,000.

                  11.3.  Amendments and Waivers. This Agreement and the exhibits
and schedules hereto set forth the entire agreement and understanding  among the
parties as to the  subject  matter  hereof and merges and  supersedes  all prior
discussions,  agreements and  understandings of any and every nature among them.
This  Agreement may be amended only by mutual  written  agreement of the Company
and the  Purchasers,  and the Company may take any action  herein  prohibited or
omit to take any action herein required to be performed by it, and any breach of
any covenant,  agreement,  warranty or representation may be waived, only if the
Company has obtained the written  consent or waiver of a majority in interest of
the  Purchasers.  No course of dealing  between or among any persons  having any
interest  in this  Agreement  will be  deemed  effective  to  modify,  amend  or
discharge any part of this  Agreement or any rights or obligations of any person
under or by reason of this Agreement.

                  11.4.  Successors  and  Assigns.  This  Agreement  may  not be
assigned by the Company except with the prior written consent of the Purchasers.
This Agreement shall be binding upon and inure to the benefit of the Company and
its permitted  successors and assigns and  Purchasers  and their  successors and
assigns.  The provisions hereof which are for Purchasers'  benefit as purchasers
or holders of the Common Shares are also for the benefit of, and enforceable by,
any subsequent holder of such Common Shares.

                  11.5. Notices.  All notices,  demands and other communications
to be given or delivered  under or by reason of the provisions of this Agreement
shall be in writing  and shall be deemed to have been given  personally  or when
mailed by certified or registered  mail,  return  receipt  requested and postage
prepaid,  and  addressed to the  addresses of the  respective  parties set forth
below or to such  changed  addresses  as such  parties may have fixed by notice;
provided,  however, that any notice of change of address shall be effective only
upon receipt:

                                       23
<PAGE>

                           If to the Company:
                           Immunomedics, Inc.
                           300 American Road
                           Morris Plains, New Jersey 07950
                           Attn: Dr. David M. Goldenberg

                           With a Copy (which shall not constitute notice) to:

                           Lowenstein Sandler PC
                           65 Livingston Avenue
                           Roseland, New Jersey 07065
                           Attn:  Peter H. Ehrenberg

                           If to the Purchasers:

                           The Aries Master Fund
                           The Aries Domestic Fund, L.P.
                           The Aries Domestic Fund II, L.P.
                           c/o Paramount Capital Asset Management, Inc.
                           787 Seventh Avenue, 48th Floor
                           New York, NY 10019
                           Attn: David M.  Tanen

                  11.6.  Governing Law; Consent to  Jurisdiction.  The validity,
performance,  construction  and effect of this  Agreement  shall be  governed by
those laws of the State of Delaware.  The parties hereto irrevocably  consent to
the jurisdiction of the courts of the State of New York and of any federal court
located in such State in connection with any action or proceeding arising out of
or relating to this Agreement, any document or instrument delivered pursuant to,
in connection with or  simultaneously  with this Agreement,  or a breach of this
Agreement or any such document or instrument.

                  11.7.  Counterparts.  This  Agreement  may be  executed in any
number of  counterparts  and,  notwithstanding  that any of the  parties did not
execute the same counterpart, each of such counterparts shall, for all purposes,
be deemed an original,  and all such  counterparts  shall constitute one and the
same instrument binding on all of the parties thereto.

                  11.8. Headings. The headings of the Sections are inserted as a
matter of  convenience  and for  reference  only and in no way define,  limit or
describe the scope of this Agreement or the meaning of any provision hereof.

                  11.9.  Severability.  In the event that any  provision of this
Agreement or the application of any provision  hereof is declared to be illegal,
invalid or otherwise  unenforceable  by a court of competent  jurisdiction,  the
remainder of this Agreement shall not be affected except to the extent necessary
to delete such illegal,  invalid or unenforceable provision unless the provision
held invalid shall substantially  impair the benefit of the remaining portion of
this Agreement.

                                       24
<PAGE>

                  11.10.  Freedom of Action. The Purchasers and their Affiliates
shall have no obligation to the Company to refrain from (i) engaging in the same
or similar  activities  or lines of business as the Company or develop or market
any products,  services or technologies  that does or may in the future compete,
directly or indirectly,  with those of the Company, (ii) investing or owning any
interest publicly or privately in, or develop a business  relationship with, any
corporation,  partnership  or other  person  or  entity  engaged  in the same or
similar  activities or lines or business as, or otherwise in  competition  with,
the Company or (iii) doing  business  with any client,  collaborator,  licensor,
consultant,  vendor or customer of the Company. It is agreed and understood that
the  preceding  sentence  shall not limit the  obligations  to the Company under
applicable  law of any person acting as a director of the Company,  nor shall it
limit the obligations of the Purchasers or their Affiliates under this Agreement
or any other agreement with the Company.

                  11.11.   Exculpation   Among   Purchasers.    Each   Purchaser
acknowledges and agrees that it is not relying upon any other Purchaser,  or any
officer, director, employee partner or affiliate of any such other Purchaser, in
making its investment or decision to invest in the Company or in monitoring such
investment.  Each Purchaser agrees that no Purchaser nor any controlling person,
officer,  director,  stockholder,  partner,  agent or employee of any  Purchaser
shall be liable for any action  heretofore  or hereafter  taken or omitted to be
taken  by any of them  relating  to or in  connection  with the  Company  or the
securities, or both.

                  11.12.  Actions by  Purchasers.  Any actions  permitted  to be
taken by holders or Purchasers of Common Shares and any consents  required to be
obtained from the same under this  Agreement,  may be taken or given only by, in
the case of  consents  or actions  requiring  approval  of a  Purchaser,  by the
applicable Purchaser,  and in all other cases, except to the extent inconsistent
with any explicit provision of this Agreement,  only by holders of a majority in
interest of the Common Shares.

                                       25
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         IN WITNESS WHEREOF,  the parties have executed this Agreement as of the
day and year first above written.

IMMUNOMEDICS, INC.                        THE ARIES MASTER FUND


By: /s/ David M. Goldenberg               By: /s/ Lindsay Rosenwald, M.D.
Name:  David M. Goldenberg                Name:  Lindsay Rosenwald, M.D.
Title: Chairman and Chief                 Title: Chairman of Paramount Capital
       Executive Officer                         Asset Management, Inc.
                                                 Investment Manager

ARIES DOMESTIC FUND, L.P.                 ARIES DOMESTIC FUND II, L.P.



By: /s/ Lindsay Rosenwald, M.D.           By: /s/ Lindsay Rosenwald, M.D.
Name:  Lindsay Rosenwald, M.D.            Name:  Lindsay Rosenwald, M.D.
Title: Chairman of Paramount Capital      Title: Chairman of Paramount Capital
       Asset Management, Inc.                    Asset Management, Inc.
       General Partner                           General Partner


LINDSAY A. ROSENWALD, M.D.                MARK C. ROGERS, M.D.



By: /s/ Lindsay Rosenwald, M.D.           By: /s/ Marc C. Rogers, M.D.
Name:  Lindsay Rosenwald, M.D.            Name:  Mark C. Rogers, M.D.


WAYNE ROTHBAUM


By: /s/ Wayne Rothbaum
Name:  Wayne Rothbaum

                                       26
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                                    EXHIBIT A



Name                                                     Initial
                                     $ Amount         Common Shares
--------------------------------  --------------    ----------------

The Aries Master Fund, a
Cayman Island exempted
Company:                            $4,672,935         1,557,645

The Aries Domestic Fund, L.P.       $1,880,460           626,820

The Aries Domestic Fund II, L.P.    $  146,601            48,867

Lindsay A. Rosenwald, M.D.          $  500,001           166,667

Mark C. Rogers, M.D.                $  100,002            33,334
Wayne Rothbaum                      $  200,001            66,667

                                       27
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