IMMUNOMEDICS INC
424B3, 1999-12-07
IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES
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PROSPECTUS                                      Filed Pursuant to Rule 424(b)(3)
                                                      Registration No. 333-90665

                               IMMUNOMEDICS, INC.

                        15,195,446 Shares of Common Stock



THE ISSUER

Immunomedics.  Inc.
300 American Road
Morris Plains, New Jersey 07950
(973) 605-8200


THE SELLING STOCKHOLDERS

The selling  stockholders  are offering to sell shares of common stock that they
may acquire  upon  conversion  of shares of our Series F  Convertible  Preferred
Stock  that we  issued to them on  December  9, 1998  pursuant  to a  Securities
Purchase  Agreement.  This prospectus  covers an additional  9,878,463 shares of
common stock in addition to the 5,316,983  shares of common stock  included in a
prior  prospectus.  Additional  information  concerning  our agreement  with the
selling  stockholders  is set forth under the caption  "Immunomedics  - December
1998 Financing."


TRADING SYMBOL

Nasdaq National Market -  "IMMU"


THE OFFERING

The selling  stockholders  may sell shares of our common stock from time to time
on the Nasdaq  National  Market at the  prevailing  market  price or in private,
negotiated  transactions.  The shares will be sold at prices  determined  by the
selling  stockholders.  We will not  receive any part of the  proceeds  from the
sale.  We are paying the expenses in  connection  with the  registration  of the
shares with the SEC. The selling stockholders may be deemed to be "underwriters"
within the meaning of the Securities  Act in connection  with the sale of shares
that they may receive upon conversion of the Series F Stock.


A purchase of shares  involves a high degree of risk. You should purchase shares
only if you can afford a complete loss of your  investment.  See "Risk  Factors"
beginning on page 4.


Neither  the  Securities  and  Exchange  Commission  nor  any  state  securities
commission  has approved or disapproved  these  securities or determined if this
prospectus  is truthful or  complete.  Any  representation  to the contrary is a
criminal offense.


                                December 6, 1999


                                        1
<PAGE>

                                Table of Contents

Risk Factors...................................................................4
         We Have a History of Operating Losses and May Never Become
           Profitable..........................................................4
         We May Not Be Able to Successfully Develop a Market for Our
           Approved Products...................................................4
         We May Not Receive Approval to Sell LeukoScan in the United
           States in a Timely Manner...........................................4
         We May Not Be Able to Bring to Market the Products We Are
           Currently Developing or Sustain Their Sales After Approval..........4
         If We Do Not Obtain Additional Capital, We May Be Required to
           Curtail Our Operations..............................................5
         Our Limited Marketing and Sales Experience and Capability
           Could Impact Our Ability to Successfully Sell Our Current
           Products............................................................5
         We May Have to Rely on Partners to Help Us Market and Sell
           Our Products Under Development......................................5
         We Could Be Temporarily Unable to Sell Our Products If Our
           Agreements with our Distributors Were Terminated....................5
         We Could Be Temporarily Unable to Sell Our Products If Our
           Agreement with our End Stage Manufacturer Was Terminated............5
         Our Internal Manufacturing Capability May Limit What We Can Sell......5
         We May Be Unable to Continue to Use Mouse Fluids for Future
           Products Which Could Require Us to Make Expensive and Time
           Consuming Changes to Our Products in Development....................6
         Our Product Development Is Dependent Upon Our Continued
           Relationship with The Center for Molecular Medicine and
           Immunology..........................................................6
         Certain Potential Conflicts of Interest Exist with The Center
           for Molecular Medicine and Immunology Which Could Affect Our
           Operations..........................................................6
         We May Not Be Able to Obtain Government Regulatory Approval in
           a Timely Manner to Market and Sell Our Products or Approval
           May Be Withdrawn....................................................6
         We Must Maintain Our Manufacturing Facilities in Accordance With
           Government Regulatory Requirements..................................7
         Changes to Health Care Reimbursement Could Adversely Affect Our
           Operations..........................................................7
         The Loss of Key Employees Could Adversely Affect our Operations.......7
         We Face Substantial Competition in the Biotechnology Field and
           May Not Be Able to Successfully Compete.............................7
         Our Products May Be Rendered Obsolete By Rapid Technological Change...7
         If We Are Unable to Protect Our Intellectual Property Rights,
           We Could Lose Our Competitive Advantage.............................8
         Our Products May Infringe Third Party Intellectual Property Rights....8
         Our Operations Could Suffer If We Are Unsuccessful in Our Pending
           Infringement Claims Concerning Our CEA Antibodies...................8
         Product Liability Claims in Excess of the Amount of Our Insurance
           Would Adversely Affect Our Financial Condition......................8
         Our Principal Stockholder Can Influence Most Matters Requiring
           Approval By Our Stockholders........................................8
         If We Are Required to Redeem the Series F Stock or Make Penalty
           Payments, Our Financial Condition Would Be Adversely Affected.......8
         Stockholders May Experience Substantial Dilution From the
           Conversion of the Series F Stock....................................9
         Short Selling of Our Common Stock Could Further Depress the
           Market Price for Our Common Stock...................................9
         Resales of Shares Held By Our Directors and Executive Officers
           May Lower the Market Price of Our Common Stock......................9
         Our Stock Price Has Been Volatile.....................................9
         Potential Loss of Our Nasdaq Listing Could Make it More Difficult
           to Sell our Shares and Affect Our Liquidity........................10
         Stockholders Could Be Adversely Affected By Our Anti-Takeover
           Provisions.........................................................10
         Our Operations Could Be Affected By Year 2000 Issues.................10
         No Expectation that We Will Pay Dividends............................10
         Special Note Regarding Forward-Looking Statements....................10

Where You Can Find More Information...........................................11

Immunomedics..................................................................12
         Description of Our Business..........................................12
         December 1998 Financing..............................................13



                                        2
<PAGE>

Use of Proceeds...............................................................17

Selling Stockholders..........................................................17

Plan of Distribution..........................................................19
         Manner of Sales; Broker-Dealer Compensation..........................19
         Filing of a Post-Effective Amendment In Certain Instances............20
         Certain Persons May Be Deemed to Be Underwriters.....................20
         Regulation M.........................................................20

Legal Matters.................................................................21

Experts  .....................................................................21






You should rely on the information incorporated by reference or provided in this
prospectus or any supplement.  We have not authorized anyone to provide you with
different  information.  You  should  not assume  that the  information  in this
prospectus  or any  supplement is accurate as of any date other than the date on
the front of such  document.  We are not  making  an offer of our  shares in any
state where the offer is not permitted.

                                       3
<PAGE>

                                  Risk Factors

     Investing in our common stock  involves a high degree of risk. As a result,
you should be able to sustain a complete loss of your investment. In addition to
the other  information in this  prospectus,  you should  carefully  consider the
following factors before purchasing any of our common stock.

We Have a History of Operating Losses and May Never Become Profitable

     We have had  significant  operating  losses since our formation in 1982 and
have not earned a profit since our inception. These operating losses and failure
to be profitable have been due mainly to the significant amount of money that we
have had to spend on research and development.  As of September 30, 1999, we had
an accumulated deficit of approximately  $101,600,000.  We expect to continue to
experience  operating  losses  until such time,  if at all,  that we are able to
generate sufficient revenues from sales of CEA-Scan(r),  LeukoScan(r) and/or our
other potential products.

We May Not Be Able to Successfully Develop a Market for Our Approved Products

     CEA-Scan  and  LeukoScan  are the only  products  which we are  licensed to
market and sell. To date,  we have received only limited  revenues from the sale
of these  products.  We cannot  assure  you that  these  products  or any of our
proposed products will achieve market acceptance or generate significant sales.

We May Not Receive Approval to Sell LeukoScan in the United States in a Timely
Manner

     We have not yet received approval from the FDA to market and sell LeukoScan
in the United  States and cannot  assure you as to when,  if ever,  that we will
obtain approval.  In addition,  the FDA could impose conditions on its approval,
which could  significantly  affect the  commercial  viability  of the product or
could require us to undertake significant additional studies or otherwise expend
additional  significant  funds. If we do not receive approval to market and sell
LeukoScan  in the  United  States  in the  near  future  or if the  FDA  imposes
significant  conditions or  restrictions,  our business and operations  could be
significantly and adversely affected.

We May Not Be Able to Bring to Market the Products We Are  Currently  Developing
or Sustain Their Sales After Approval

     Before any of our products that we are currently developing can be marketed
and sold,  we must  undertake  substantial  research  and  development.  All new
products face a high degree of uncertainty, including the following:

*    We may not receive regulatory approval to perform human clinical trials for
     the products we currently have planned or we may be unable to  successfully
     complete our ongoing clinical trials.

*    The  results  from  preclinical  studies  and  clinical  trials  may not be
     indicative of results that will be obtained in later-stage testing.

*    We may be unable to timely recruit a sufficient  number of patients for our
     clinical  trials.  Delays  in  planned  patient  enrollment  may  result in
     increased costs and delays.

*    We may be unable to obtain  approval  from the FDA and  comparable  foreign
     authorities  because we are unable to demonstrate  that the product is safe
     and effective for the intended  use, or obtaining  regulatory  approval may
     take  significantly  more time and cost  significantly  more  money than we
     currently anticipate.

*    We may discover that the product has undesirable or unintended side effects
     or other characteristics that make it impossible or impracticable for us to
     continue development or which may limit the product's commercial use.

*    We do not expect that any new product  which is  currently  in research and
     development will be commercially available for at least several years.

*    We may be unable to produce the product in commercial quantities at
     reasonable cost.



                                        4
<PAGE>

*    We may  be  unable  to  successfully  market  the  product  or to  find  an
     appropriate corporate partner, if necessary,  to assist us in the marketing
     of the product.

*    The product may not gain satisfactory market acceptance.

*    The product may be superceded  by another  product  commercialized  for the
     same  indication  or may  infringe  patents  issued to others,  which would
     prevent us from marketing and selling the product.

*    After  approval,  the product may be recalled or withdrawn at any time as a
     result  of  regulatory  issues,   including  those  concerning  safety  and
     efficacy.

     If we are unable to continue to develop  products that we can  successfully
market,  our business,  financial  condition  and results of operations  will be
significantly and adversely affected.

If We Do Not Obtain Additional Capital, We May Be Required to Curtail Our
Operations

     Without a  significant  increase in product  revenues or other  infusion of
capital  during our  current  fiscal year which ends June 30,  2000,  we will be
required to significantly reduce our operating expenses, including the amount of
resources  devoted to  marketing  and sales,  product  development  and clinical
trials,  which  could have a  significant  and  adverse  effect on us. We cannot
assure you that any  additional  financing  will be available to us at all or on
terms we find  acceptable  or that the  terms of any  financing  will not  cause
substantial dilution to our existing stockholders.

Our Limited Marketing and Sales Experience and Capability Could Impact Our
Ability to Successfully Sell Our Current Products

     We are relying, in substantial part, on our own limited sales and marketing
organization to market CEA- Scan and LeukoScan. We cannot assure you that we can
successfully maintain and continue to build our sales force. If we are unable to
continue to build and maintain  our sales force,  our  financial  condition  and
operating results may be significantly and adversely affected.

We May Have to Rely on Partners to Help Us Market and Sell Our Products Under
Development

     The marketing and sale of our proposed  products may be dependent  upon our
entering into arrangements with corporate partners. We cannot assure you that we
will be successful in forming these  relationships or that these  relationships,
even if formed, will be successful.

We Could Be Temporarily Unable to Sell Our Products If Our Agreements with our
Distributors Were Terminated

     We currently do not have the resources to  internally  develop and maintain
the operating  procedures  required by the FDA and comparable foreign regulatory
authorities  to  oversee  distribution  of our  products.  As a result,  we have
entered into  arrangements  with third  parties to perform this function for the
foreseeable  future. If these agreements are terminated,  we will be required to
enter into arrangements with other government approved third parties in order to
be able to distribute our products.  We will be unable to continue to distribute
our products until an acceptable alternative is identified. If we were even only
temporarily   unable  to  distribute   our  products,   our  business  could  be
significantly and adversely effected.

We Could Be Temporarily Unable to Sell Our Products If Our Agreement with our
End Stage Manufacturer Was Terminated

     We rely on a single third party to perform  certain  end-stage  portions of
the  manufacturing  process for CEA-Scan and LeukoScan which we are unable or do
not  have  the  resources  to  perform.  If this  third  party  were  to  become
unavailable,  we would be unable to complete the manufacturing  process until we
entered into an agreement with another  qualified  entity. We cannot assure that
we will be able to  negotiate  an  agreement  with  another  entity  on terms we
consider  acceptable,  if at all. Even if we were able to do so, any substantial
delay in our  ability  to  manufacture  our  products  could  significantly  and
adversely affect our operations.

Our Internal Manufacturing Capability May Limit What We Can Sell



                                        5
<PAGE>

     If demand  for our  approved  product  increases  significantly,  we cannot
assure you that we will continue to have the capacity to manufacture  commercial
quantities successfully.  In addition, if any of our other products are approved
for  marketing  and sale, we cannot assure you that we will continue to have the
capacity and expertise to manufacture commercial quantities of multiple products
successfully or with acceptable profit margins. If we were even only temporarily
unable to manufacture  sufficient quantities of our products to meet demand, our
business could be significantly and adversely effected.

We May Be Unable to Continue to Use Mouse Fluids for Future Products Which Could
Require Us to Make Expensive and Time Consuming Changes to Our Products in
Development

     CEA-Scan and certain of our other  imaging  agents are derived from ascites
fluid produced in mice.  Regulatory  authorities,  particularly in Europe,  have
expressed  concerns about the use of mice fluid for the production of monoclonal
antibodies. We cannot assure you that regulatory authorities will agree that our
quality control  procedures will be adequate for future  products.  While we are
continuing  our  development  efforts  to  produce  certain  of  our  monoclonal
antibodies  using cell culture methods,  this process  constitutes a substantial
production change, which will require additional manufacturing equipment and new
regulatory  approval.  We cannot  assure you that we will have the  resources to
acquire the  additional  manufacturing  equipment  and resources or that we will
receive the required  regulatory  approval on a timely basis, if at all. We also
have contracted with a third party for the development and production of certain
humanized  antibodies,   but  we  cannot  assure  that  these  efforts  will  be
successful.

Our Product Development Is Dependent Upon Our Continued Relationship with The
Center for Molecular Medicine and Immunology

     The Center for Molecular Medicine and Immunology,  a not-for-profit  cancer
research  center,  performs  pilot and  pre-clinical  trials in product areas of
importance to us. CMMI also conducts basic research and patient evaluations in a
number of areas of  potential  interest to us. If CMMI were no longer to provide
these  services,  we would  have to make  alternative  arrangements  with  third
parties which could  significantly  delay and increase expenses  associated with
pre-clinical testing and initial clinical trials.

Certain Potential Conflicts of Interest Exist with The Center for Molecular
Medicine and Immunology Which Could Affect Our Operations

     Dr. David M. Goldenberg,  our Chairman and Chief Executive Officer,  is the
founder, President and a member of the Board of Trustees of CMMI. Dr. Goldenberg
devotes more of his time  working for CMMI than for us. In  addition,  other key
personnel currently have  responsibilities both to CMMI and us. As a result, the
potential  for  conflict of interest  exists and  disputes  could arise over the
allocation of research projects and ownership of intellectual property rights.

We May Not Be Able to Obtain Government Regulatory Approval in a Timely Manner
to Market and Sell Our Products or Approval May Be Withdrawn

     Regulation  by  governmental  authorities  in the United States and foreign
countries  is a  significant  factor in the  manufacture  and  marketing  of our
presently marketed and proposed products as well as our research and development
activities.  All of our proposed  products will require  regulatory  approval by
governmental  agencies prior to commercialization  and our products must undergo
rigorous   preclinical  and  clinical  testing  and  other  premarket   approval
procedures by the FDA and comparable  foreign  authorities.  In addition,  since
certain of our potential  products involve the application of new  technologies,
regulatory  approvals  may take longer  than for  products  produced  using more
conventional  methods.  Once we begin  clinical  trials for a new  diagnostic or
therapeutic  product,  it may  take  five to ten  years or more to  receive  the
required  regulatory  approval to commercialize that product and begin to market
it to the  public.  Various  federal  and,  in some cases,  state  statutes  and
regulations  also  govern or  influence  the  manufacturing,  safety,  labeling,
storage,  record keeping and marketing of these products. The lengthy process of
seeking these approvals,  and the subsequent compliance with applicable statutes
and regulations,  will require us to expend substantial resources. If we fail to
obtain  or  are  otherwise   substantially  delayed  in  obtaining,   regulatory
approvals,  our business and  operations  could be  significantly  and adversely
affected.

     In responding to a new drug application, or a biologic license application,
government   regulators  may  grant  marketing  approvals,   request  additional
information or further  research,  or deny the application if it determines that
the application does not satisfy its regulatory approval criteria. Approvals may
not be granted on

                                        6
<PAGE>

a  timely  basis,  if at all,  or if  granted  may not  cover  all the  clinical
indications  for  which  we are  seeking  approval  or may  contain  significant
limitations  in the form of  warnings,  precautions  or  contraindications  with
respect to conditions of use. Even after approval,  we may be required to recall
or withdraw a product as a result of subsequently  discovered safety or efficacy
concerns.

Our Business Involves the Use of Hazardous Materials

     In  addition  to laws and  regulations  enforced  by the  FDA,  we are also
subject to regulation under various other foreign,  federal, state or local laws
and  regulations.  Our research and  development  involve the  controlled use of
hazardous materials,  chemicals,  viruses and various radioactive compounds. The
risk of  accidental  contamination  or injury  from  these  materials  cannot be
completely  eliminated.  If an accident occurs,  we could be held liable for any
damages that result and any liability could exceed our resources.

We Must Maintain Our Manufacturing Facilities in Accordance With Government
Regulatory Requirements

     Our facilities are subject to inspection by the FDA and comparable  foreign
authorities. A separate license is sometimes required for commercial manufacture
of any product.  Failure to maintain  these  licenses or to meet the  regulatory
inspection  criteria would result in disruption to our  manufacturing  processes
and could have a significant and adverse effect on our business and operations.

Changes to Health Care Reimbursement Could Adversely Affect Our Operations

     Our ability to successfully  commercialize our products will depend in part
on the extent to which  reimbursement  for the cost of our  products and related
treatment will be available from government health  administration  authorities,
private health insurers and other  organizations.  These third-party  payers are
increasingly  challenging  the price of medical  products and services.  Several
proposals have been made that may lead to a government-directed  national health
care system.  Adoption of this type of system could further limit  reimbursement
for  medical  products,  and we  cannot  assure  you that  adequate  third-party
coverage will be available to enable us to maintain  price levels  sufficient to
realize an  appropriate  return on our  investment  in product  development.  In
addition,  we also  cannot  assure  you  that  the U.S.  government  or  foreign
governments  will not  implement a system of price  controls.  Any system  might
significantly   and  adversely   affect  our  ability  to  market  our  products
profitably.

The Loss of Key Employees Could Adversely Affect our Operations

     As a small biotechnology company, we are heavily dependent upon the talents
of Dr. Goldenberg and certain key scientific personnel. If Dr. Goldenberg or any
of  our  other  key  personnel  leave  our  employ,   our  operations  could  be
significantly and adversely affected.  In addition,  from time to time we have a
need  to  expand  our  management  and  scientific  personnel.  Competition  for
qualified  personnel  in the  biotechnology  and  pharmaceutical  industries  is
intense and we cannot assure you that we will be  successful in our  recruitment
efforts.  If we are  unable  to  retain  or,  when  needed,  attract  additional
qualified  personnel,  our operations also could be significantly  and adversely
affected. We Face Substantial Competition in the Biotechnology Field and May Not
Be Able to Successfully Compete

     The biotechnology industry is highly competitive,  particularly in the area
of cancer  diagnostic  and  therapeutic  products.  We are  likely to  encounter
significant  competition  with respect to our  existing  products as well as our
products  currently  under  development.  A number of companies,  including IDEC
Pharmaceuticals,  Genentech,  SmithKline Beecham,  Nycomed Amersham, and Coulter
Pharmaceutical,  are engaged in the  biotechnology  field, and in particular the
development  of  cancer  diagnostic  and  therapeutic  products.  Many of  these
companies  have  significantly   greater  financial,   technical  and  marketing
resources  than  us.  In  addition,  many  of  these  companies  may  have  more
established positions in the pharmaceutical  industry and may be better equipped
than us to develop, refine and market their products.

     We also expect to face increasing  competition from  universities and other
non-profit  research  organizations.  These institutions carry out a significant
amount of research and  development in the field of  antibody-based  technology.
These institutions are becoming  increasingly more aware of the commercial value
of their  findings  and more  active in  seeking  patent  and other  proprietary
rights, as well as licensing revenues.


                                        7
<PAGE>


Our Products May Be Rendered Obsolete By Rapid Technological Change

     We are  pursuing  an area of  product  development  in  which  there is the
potential for extensive technological innovations in relatively short periods of
time. We cannot assure you that our  competitors  will not succeed in developing
products that are safer or more effective than our products. Rapid technological
change or developments  by others may result in our current  products as well as
those in development becoming noncompetitive or obsolete.

If We Are Unable to Protect Our Intellectual Property Rights, We Could Lose Our
Competitive Advantage

     Our  commercial   success  is  highly  dependent  upon  patents  and  other
proprietary  rights  that we own or license.  We cannot  assure you that our key
patents  will  not be  invalidated  or  will  provide  us  protection  that  has
commercial  significance.  Litigation  may be  necessary  to protect  our patent
positions,  which could be costly and time consuming.  If any of our key patents
that we own or license are invalidated,  our business may be  significantly  and
adversely  affected.  In addition,  other  companies may  independently  develop
similar  trade  secrets  or  know-how  or obtain  access  to our trade  secrets,
know-how or  proprietary  technology,  which could  significantly  and adversely
affect our business.

Our Products May Infringe Third Party Intellectual Property Rights

     Other  companies  may have filed  applications  for,  or have been  issued,
patents  and  obtained  other  proprietary  rights  to  technology  which may be
potentially useful to us. Since we do not have the resources to maintain a staff
whose primary  function is to  investigate  the level of protection  afforded to
third  parties on devices and  components  which we use in our  products,  it is
possible that a third party could  successfully claim that our products infringe
on their intellectual  property rights. If this were to occur, we may be subject
to substantial damages, and we may not be able to obtain appropriate licenses at
a cost we could  afford and we may not have the ability to timely  redesign  our
products.  If we are  required  to pay  damages  or are  unable to obtain  these
rights, our business could be significantly and adversely  affected.  Even if we
are successful in defeating any alleged  infringement  claims,  litigation could
result in a substantial diversion of managerial time and resources,  which could
be better and more fruitfully utilized on other activities.

Our Operations Could Suffer If We Are Unsuccessful in Our Pending Infringement
Claims Concerning Our CEA Antibodies

     We are  involved in certain  litigation  with F.  Hoffmann-LaRoche  and its
affiliates concerning the validity our European patents covering the antibody we
use in our CEA-Scan  cancer imaging product and our CEA- Cide(tm) cancer therapy
product,  as well as the use of highly specific anti-CEA antibodies for a number
of other uses. We have claimed that they have infringed our patent and they have
counter-claimed  seeking to nullify the patents that were issued.  If we receive
an  unfavorable  outcome  in  any  of  these  matters,  our  business  could  be
significantly and adversely affected.

Product Liability Claims in Excess of the Amount of Our Insurance Would
Adversely Affect Our Financial Condition

     The  clinical   testing,   marketing  and  manufacturing  of  our  products
necessarily  involve  the risk of product  liability.  While we  currently  have
product  liability  insurance,  we cannot  assure that we will be able to obtain
insurance in the future at an acceptable  cost, if at all. If we cannot maintain
our existing or comparable liability  insurance,  our ability to test clinically
and market our products may be significantly impaired.  Moreover, the amount and
scope  of our  insurance  coverage  or  indemnification  arrangements  with  any
distributor or other third party upon which we rely may be inadequate to protect
us in the event of a successful  product liability claim. Any claim in excess of
the amount any insurance we then had could  significantly  and adversely  affect
our financial condition.

Our Principal Stockholder Can Influence Most Matters Requiring Approval By Our
Stockholders

     As of December 6, 1999, Dr.  Goldenberg,  our Chairman and Chief  Executive
Officer,  controlled  the right to vote  over  approximately  30% of our  common
stock. As a result of this voting power, Dr.  Goldenberg may have the ability to
determine the election of all of our directors,  direct our policies and control
the  outcome  of  substantially  all  matters  which may be put to a vote of our
stockholders.


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<PAGE>

If We Are Required to Redeem the Series F Stock or Make Penalty Payments, Our
Financial Condition Would Be Adversely Affected

     As discussed below in the section  "Immunomedics - December 1998 Financing"
upon the occurrence of certain  circumstances,  we may be required to redeem the
Series F Stock or pay significant penalties. These penalties could be as much as
15% per year of the stated value of the Series F Stock.  We also may be required
to reduce the  conversion  price of the Series F Stock.  If we are  required  to
redeem  the  Series F Stock or make the  penalty  payments,  we may not have the
financial ability to make these payments. Even if we have the financial ability,
these payments could  significantly and adversely affect our financial condition
and deplete our cash resources.

Stockholders May Experience Substantial Dilution From the Conversion of the
Series F Stock

     Because the conversion  price of the Series F Stock is not fixed, we may be
required to issue to the holders of the Series F Stock a  significant  number of
shares of our common stock.  The conversion price generally will be the lower of
$2.50 and the average  closing bid price of our common  stock over the lowest 15
days during the 45-day period  immediately  prior to the  applicable  conversion
date.  As of December 6, 1999,  the  conversion  price would have been $1.18 per
share and we would have been required to issue approximately 6,335,014 shares of
our common stock had the holders  converted all of their  remaining  outstanding
Series F Stock on this date. If our stock price decreases,  we would be required
to issue an increased number of shares and the greater the decline in the market
price,  the  greater  the  number of shares we would be  required  to issue upon
conversion of our Series F Stock.

     Given  that the  conversion  price is based on the  average  of the  lowest
closing price during a specified  period,  the market price for our common stock
may be significantly greater than the conversion price for the Series F Stock in
effect at the time of conversion.  In this case, the conversion of a significant
number  of  Series  F  Stock  into  common   stock   during  that  period  would
significantly  dilute the percentage  ownership  interest of our existing common
stockholders.

Short Selling of Our Common Stock Could Further Depress the Market Price for Our
Common Stock

     Subject to the limitations described below in "Immunomedics - December 1998
Financing,"  the holders of the Series F Stock are  permitted  to sell short our
common  stock;  that is sell  shares of common  stock that they do not own.  The
selling  stockholders could then convert their Series F Stock and use the shares
of common stock  received  upon  conversion to cover their short  position.  The
perception  that the selling  stockholders  may sell short our common  stock may
cause  others to sell their  shares as well.  An increase in the sales volume of
our common  stock,  whether  short sales or not and whether the sales are by the
selling  stockholders or others, could potentially cause the market price of our
common stock to decline further.  Since the Series F Stock became convertible in
June 1999, the monthly reported short position in our common stock had increased
250% from 575,000 at June 15, 1999 to its high of  2,103,000  at  September  15,
1999 and as of November 15, 1999, the short position was 1,291,399.

Resales of Shares Held By Our Directors and Executive Officers May Lower the
Market Price of Our Common Stock

As of  December 6, 1999,  we had a total of  42,517,107  shares of common  stock
outstanding,  7,130,272  of  which  were  held by our  directors  and  executive
officers.  These shares may only be resold in limited quantities and only within
the limitations  imposed by Rule 144 under the Securities Act. The mere prospect
that these  shares may be publicly  resold  could lower the market price for our
common stock.

Our Stock Price Has Been Volatile

     We believe  that a variety of factors  have caused the market  price of our
common stock to fluctuate substantially,  and that it will continue to fluctuate
in the future. These factors include:

*    actual or anticipated fluctuations in our operating results;

*    the status of our products in development;

*    new products or technical innovations by us or by our existing or potential
     competitors;


                                        9
<PAGE>


*    the formation or termination of our corporate alliances and distribution
     arrangements;

*    prolonged periods of regulatory review of new products or new uses for
     existing products;

*    determinations regarding our patent applications and those of others;

*    trading strategies occurring in the market place with respect to our common
     stock; and

*    general market conditions and other factors unrelated to us or outside our
     control.

Potential Loss of Our Nasdaq Listing Could Make it More Difficult to Sell our
Shares and Affect Our Liquidity

     If the bid price of our common stock were to fall below $1.00 per share, if
we were to have less than  $4,000,000 in net tangible  assets (total assets less
total liabilities and goodwill), or if the value of our common stock held by our
stockholders  (other than our directors and executive  officers) were to be less
than  $5,000,000,  our common  stock  could be  delisted  from The Nasdaq  Stock
Market.  If our common stock were  delisted from Nasdaq,  trading if any,  would
thereafter be conducted in the over-the-counter  market. This would make it more
difficult for an investor to dispose of, or to obtain  accurate  quotations for,
our common  stock.  Additionally,  it may become more  difficult for us to raise
funds through the sale of our  securities.  Finally,  as discussed  elsewhere in
this prospectus,  a delisting of our common stock would also give the holders of
the Series F Stock certain redemption rights.

Stockholders Could Be Adversely Affected By Our Anti-Takeover Provisions

     Our board of directors has the  authority,  without any further vote by our
stockholders, to issue up to 10,000,000 shares of preferred stock in one or more
series and to determine  the  designations,  powers,  preferences  and relative,
participating,  optional or other rights  thereof,  including the dividend rate,
whether dividends are cumulative,  conversion rights,  voting rights, rights and
terms of redemption,  redemption price and liquidation  preference.  Issuance of
preferred  stock could have the effect of delaying,  deterring  or  preventing a
change in control of our company,  or could impose various  procedural and other
requirements  that could make it more  difficult for holders of our common stock
to effect certain corporate actions,  including the ability to replace incumbent
directors  and to  accomplish  transactions  opposed by the  incumbent  board of
directors.  The rights of the  holders of our common  stock would be subject to,
and may be  adversely  affected  by, the rights of the holders of any  preferred
stock that may be issued in the future.

Our Operations Could Be Affected By Year 2000 Issues

     We have completed a review of our business systems,  including our computer
systems and  manufacturing  equipment,  and have sent  written  inquiries to our
customers,  distributors  and vendors as to their  progress in  identifying  and
addressing  problems that their systems may face in correctly  interpreting  and
processing date information as the year 2000 approaches and is reached. We could
encounter  problems with supplier  and/or revenue sources which could affect us.
We cannot  accurately  predict the occurrence or outcome of any these  problems,
nor can we estimate the dollar amount of these problems.  In addition, we cannot
assure you that a failure by a third party to ensure year 2000  compliance  will
not significantly and adversely effect us.

No Expectation that We Will Pay Dividends

     We have never paid any dividends on our common stock.  For the  foreseeable
future,  we expect to retain  earnings,  if any,  to finance the  expansion  and
development of our business.  Any future payment of dividends will be within the
discretion  of our Board of Directors and will depend upon a variety of factors,
including  our  earnings,  capital  requirements,  and  operating  and financial
condition. In addition, we are required to obtain the approval of the holders of
the Series F Stock prior to the payment of any dividends on our common stock.

Special Note Regarding Forward-Looking Statements

     We  have  made  statements  in this  prospectus,  and in the  documents  we
incorporate  by  reference,  that are  "forward-looking  statements"  within the
meaning of the Securities Act and the Securities Exchange Act.


                                       10
<PAGE>

Sometimes  these  statements  contain  words like  "may,"  "believe,"  "expect,"
"continue,"  "intend,"  "anticipate"  or other similar words.  These  statements
could  involve  known and unknown  risks,  uncertainties  and other factors that
might  significantly  alter the actual results  suggested by the statements.  In
other  words,   our   performance   might  be  quite  different  from  what  the
forward-looking  statements  imply.  The  following  factors,  as well as  those
discussed  above in this "Risk  Factors"  section and in the documents  which we
incorporate by reference, could cause our performance to differ from the implied
results:

         *        inherent uncertainties accompanying the marketing of CEA-Scan
                  and LeukoScan.

         *        inherent uncertainties involving new product development and
                  marketing.

         *        inability to obtain capital for continued product development
                  and commercialization.

         *        actions of regulatory authorities concerning product approval.

         *        actions of government and private organizations concerning
                  reimbursement of medical expenses.

         *        impact of competitive products and pricing.

         *        results of clinical trials.

         *        loss of key employees.

         *        changes in general economic and business conditions.

         *        changes in industry trends.

     We have no  obligation  to release  publicly the result of any revisions to
any of our "forward-looking  statements" to reflect events or circumstances that
occur after the date of this  prospectus  or to reflect the  occurrence of other
unanticipated events.


     Where You Can Find More Information

     We publicly file annual,  quarterly and current  reports,  proxy statements
and other  documents with the SEC. You may read and copy any of these  documents
at the SEC's  public  reference  rooms in  Washington,  D.C.,  New York City and
Chicago.  Please call the SEC at 1-800-SEC-0330  for further  information on the
public   reference   rooms.   The  SEC   maintains   a   Internet   website   at
http://www.sec.gov where our publicly filed documents may be obtained.

     This prospectus is part of a registration statement filed with the SEC. Our
registration  statement contains more information than this prospectus regarding
us and our common stock and includes  supplemental  exhibits and schedules.  You
can  obtain a copy of the  registration  statement  from the SEC at the  address
listed above or from its Internet website.

     The SEC allows us to  "incorporate  by reference"  into this prospectus the
information we file with it. This means that we are deemed to be disclosing such
information  to you by referring you to those  documents.  This  information  is
important and should be reviewed.  The information  incorporated by reference is
considered to be part of this  prospectus,  and later  information  that we file
with the SEC will  automatically  update and supercede the  information  in this
prospectus.

     We incorporate by reference into this prospectus the documents listed below
and any future filings we make with the SEC under Sections  13(a),  13(c), 14 or
15(d) of the Securities Exchange Act:

         *        Annual Report on Form 10-K for the fiscal year ended June 30,
                  1999;

         *        Proxy Statement, dated October 18, 1999, with respect to our
                  1999 annual meeting of stockholders;



                                       11
<PAGE>

               -        Quarterly Report on Form 10-Q for the fiscal quarter
                        ended September 30, 1999;

               -        Current Report on Form 8-K, dated November 24, 1999; and

         *        Description  of the common  stock  contained  in Item 1 of our
                  Registration Statement on Form 8-A, dated May 7, 1984.

     You may request a copy of these  filings,  at no cost,  by contacting us at
the following address:

                  Immunomedics, Inc.
                  300 American Road
                  Morris Plains, New Jersey 07950
                  (973) 605-8200
                  Attention: Investor Relations


     Immunomedics

Description of Our Business

     We  are a  biopharmaceutical  company,  which  develops,  manufactures  and
markets  products for the detection and treatment of cancers and other diseases.
These  products,  which are based on our  monoclonal  antibody  technology,  are
designed to deliver  radioisotopes,  chemotherapeutic  agents,  toxins,  dyes or
other substances to a specific disease site or organ system.

     We have received  approval from the respective  regulatory  agencies in the
United States, the 15 member countries of the European Union, Canada and certain
other countries to market and sell CEA-Scan  (arcitumomab),  our imaging product
for the detection of recurrent and/or metastatic colorectal cancer.

     We also have received  approval to market and sell  LeukoScan  (sulesomab),
our  imaging  product  for  detection  and  diagnosis  of  osteomyelitis   (bone
infection) in long bones and in diabetic foot ulcer  patients,  in the 15 member
countries of the European  Union.  We have filed an application  with the FDA in
the U.S. and the comparable  regulatory  agency in Canada for approval to market
LeukoScan for imaging of infection in  osteomyelitis  as well as for the imaging
of infection in acute, atypical  appendicitis.  We have been advised by FDA that
there are still  deficiencies  with our application  relating to the adequacy of
our data necessary to support final approval for these indications.  Despite our
confidence  that we were  making  progress  with  FDA  and  had  adhered  to all
agreements and  guidelines,  it is now clear to us that we need to take whatever
steps are  available  to us to gain a more  receptive  audience in order to gain
marketing approval for this product.  We can not assure you that we will receive
FDA approval for this product in a timely manner, or at all.

     Marketing, Sales and Distribution

     CEA-Scan is marketed and sold in the U.S.  directly by our limited internal
sales force,  who are focused on new  customers in major  medical  centers.  Our
skilled  nuclear  medicine  technicians  work with this sales  force and provide
technical support directly to our customers. We have entered into a distribution
arrangement in the U.S. with Integrated  Commercialization Solutions, a division
of Bergen Brunswig  Corporation,  to provide product support services  including
customer service, order management,  distribution,  invoicing and collection. We
also have agreement with Syncor  International,  the world's leading provider of
radiopharmacy  services,  under which  Syncor  makes  CEA-Scan  available to its
hospital and clinic  accounts  throughout  the U.S.,  supported by our sales and
technical support specialists.

     Our  European  operations,  headquartered  in  Hillegom,  The  Netherlands,
include  European  management,   sales  and  marketing,   customer  service  and
invoicing,   collection  and  other  administrative   functions.  We  also  have
established  sales  representation  in most major European  markets.  We service
other markets  through the appointment of local  distributors  who provide sales
and  marketing  support  as  well  as  local  product  distribution.  We have an
agreement with Eli Lilly Deutschland GmbH to package and distribute our products
throughout the 15 member countries of the European Union and other countries.

     Imaging Products



                                       12
<PAGE>

     Our  imaging  products  involve  injecting  a patient  with a  radioisotope
attached to an  antibody  fragment.  An antibody is a protein  that can find and
attach  itself to a specific  substance  called an antigen.  These  antigens are
present  on tumor  cells,  white  blood  cells that  accumulate  at the sites of
infections,   and  other  disease  entities.   A  radioisotope   attached  to  a
disease-targeting  antibody  is  delivered  to a  disease  site for  imaging.  A
standard  nuclear  medicine  imaging  camera is then used to detect and  display
radioisotope concentrations at various sites of disease.

     The  antibody  fragment in CEA-Scan  is directed  against  carcinoembryonic
antigen  (CEA),  which is abundant at the site of  virtually  all cancers of the
colon or rectum,  whether they are primary tumors or which have spread. CEA also
is  associated  with many other  cancers.  We are  conducting  phase IV clinical
trials to evaluate the product following repeated  administration.  We also have
been  performing  clinical  trials  using CEA- Scan for imaging  lung cancer and
breast  cancer.  We are  discussing  the results of these  clinical  trials with
European regulatory authorities to determine whether these data will support the
submission  of  applications  for  marketing  approval.   In  addition,  we  are
continuing our efforts in developing cancer detection applications with CEA-Scan
utilizing  hand-held  radiation-detecting  probes for use in  colorectal  cancer
surgery.

     LeukoScan is a monoclonal antibody fragment,  which seeks out, and binds to
white blood cells  (granulocytes)  associated  with a potentially  wide range of
infectious and inflammatory diseases.

     We are  studying  the  following  two other  imaging  products  pursuant to
Investigational  New Drug  applications  that we have filed or plan to file with
the FDA and we have ongoing clinical trials in Europe:

*    LymphoScan(r), for non-Hodgkin's B-cell lymphomas.

*    AFP-Scan(r), for liver cancer and germ-cell tumors of the ovaries and
     testes.

     Therapeutic Products

     We are  applying  our  expertise in antibody  selection,  modification  and
chemistry  to cancer  therapeutics,  using  monoclonal  antibodies  labeled with
therapeutic radioisotopes or conjugated with drugs. We are engaged in developing
anti-cancer  products,  principally with a technique called  radioimmunotherapy.
This technique may deliver  radiolabeled  therapeutic agents to tumor sites more
selectively  than  current  radiation  therapy  technologies,  while  minimizing
debilitating side effects. In addition, we are evaluating in clinical trials the
effects of our  non-radioactive  lymphoma  antibody  in  non-Hodgkin's  lymphoma
patients.

     Research Programs

     In addition to  concentrating on our products in clinical  development,  we
conduct ongoing research in many related areas. We conduct research in-house and
in  collaboration  with The Center for Molecular  Medicine and  Immunology  also
known as the Garden State Cancer Center and other academic and research centers.
In March 1999, we entered into a joint  venture with Beckman  Coulter to develop
the next generation of cancer  therapeutics  using  bi-specific  antibodies.  We
believe our ongoing research efforts will identify new and improved products and
techniques for diagnosing and treating various cancers and infectious diseases.

     Our  research  efforts  are  focused in various  areas  related to our core
technology,  including  antibody  engineering  and the  identification  of other
antibody-directed  approaches  to  cancer  therapy.  We  have  made  significant
progress in  humanizing  certain  mouse  antibodies  and have  reengineered  the
humanized antibodies with improved  characteristics.  We are continuing our work
on  selective  coupling  of  therapeutic  site  specific  agents  onto  antibody
fragments  which  will  offer the  advantage  of  loading  multiple  therapeutic
compounds  onto  antibodies  at a particular  disease  site. We also continue to
investigate pre-targeting whereby an antibody is administered first, followed by
a radionuclide or drug administration.

     We  also  are   continuing   our  research  into  the  use  of  alternative
radioisotopes, such as Yttrium-90 in place of Iodine-131. Our research indicates
that  Yttrium-90 is retained by lymphoma cells for longer periods after antibody
metabolism,  and shows greater  efficacy  against  larger  tumors.  We also have
developed a technology using a compound called "DOTA" to tightly bind Yttrium-90
to antibodies.

     In addition,  we are  continuing  our efforts to scale-up  our  proprietary
method for technetium-99m radiolabeling of peptides, using single-vial kits.



                                       13
<PAGE>

December 1998 Financing

     On December 9, 1998,  we  completed a private  placement of 1,250 shares of
Series F Convertible  Preferred Stock to the selling  stockholders  and received
gross proceeds of $12,500,000.

     Each share of Series F Stock has an initial stated value of $10,000,  which
increases at the rate of 4% per annum and as of December 6, 1999 equaled $10,397
per share. The Series F Stock became  convertible on June 8, 1999. The number of
shares of common stock issuable upon  conversion of each share of Series F Stock
will be  determined by dividing the stated value of $10,000 plus an accretion of
4% per annum,  by the conversion  price then in effect.  As of December 6, 1999,
531.5 shares of the Series F Stock had been converted  into 4,683,017  shares of
common stock.

     The conversion price is equal to:

*    the Variable  Price, if the Variable Price is less than the "Trigger Price"
     of $2.50; except that prior to December 9, 1999, subject to acceleration in
     certain  instances,  if the  Variable  Price is greater than $1.80 and less
     than $2.50, the conversion price will equal $2.50; or

*    $2.50, if the Variable Price is equal to or greater than the $2.50 and less
     than or equal to $3.75; or

*    $2.50 plus  one-half of the amount,  if any,  by which the  Variable  Price
     exceeds $3.75, if the Variable Price is greater than $3.75.

     The  $2.50  "Trigger  Price"  was set based on 125% of the  "Initial  Fixed
Price" of $2.00,  which was the average  closing  bid price of our common  stock
during the 20 consecutive  trading days ended June 6, 1999. The "Variable Price"
is equal to the average of the 15 lowest closing bid prices for our common stock
during the 45 trading  days  immediately  preceding  a  conversion  date.  As of
December 6, 1999, the Variable Price was $1.18 per share.

     At any time during the 90-day  period  commencing  on December 6, 1999,  we
may, require the selling stockholders to purchase up to an additional $7,500,000
million  (750  shares) of our Series F Stock.  Our right to require  the selling
stockholders to purchase this additional amount is subject to certain conditions
and  limitations,  including  that the Variable Price has been at least equal to
$2.00 for a specified period of time. Given the recent price at which our common
stock has traded, it is unlikely that this condition will be satisfied.  We have
granted the selling  stockholders  certain  participation rights if we issue any
future floating rate convertible  securities.  The holders of the Series F Stock
generally  do not have the right to vote for the  election  of  directors  or on
other matters, except to the extent their rights would be adversely affected.

     Upon the  occurrence  of certain  events,  we may be required to redeem the
Series F Stock, pay certain penalties and/or adjust the conversion price.  These
events include the following:

*    If we consolidate,  merge or otherwise combine with another entity and as a
     result the stockholders of our company immediately prior to the transaction
     do not retain  sufficient  voting power to elect a majority of the board of
     directors of the new or combined  entity,  then the holders of the Series F
     Stock may require us to redeem  their  shares at a price per share equal to
     the greater of

     (1) 125% of the stated value of $10,000 per share plus the  accretion of 4%
     per annum, and

     (2) the value of our common stock that would be issuable upon conversion of
     the Series F Stock.

          However,  if the consolidation,  merger or other business  combination
     occurs  as a result  of a proxy  solicitation  which  was not  approved  or
     recommended by our Board of Directors,  then, if the holders exercise their
     redemption rights, we may, in lieu of redemption,

     (y) readjust the Initial  Fixed Price to the lower of (A) 80% of the lowest
     Variable Price during the period  beginning on the date the solicitation is
     announced and ending on the date the solicitation is consummated, abandoned
     or terminated or (B) the Initial Fixed Price then in effect, and

     (z) pay a penalty  of 1% per day of the stated  value of $10,000  per share
     plus the  accretion of 4% per annum for a maximum of 10 days in any 365-day
     period.


                                       14
<PAGE>

*    If at least a  specified  percentage  of the  holders of our  common  stock
     accept a purchase, tender or exchange offer, then the holders of the Series
     F Stock may require us to redeem their shares at a price per share equal to
     the greater of

     (1) 125% of the stated value of $10,000 per share plus the  accretion of 4%
     per annum, and

     (2) the value of our common stock that would be issuable upon conversion of
     the Series F Stock.

          However, if the purchase, tender or exchange offer was not approved or
     recommended by our Board of Directors;  then, if the holders exercise their
     redemption rights, we may, in lieu of redemption,

     (y) readjust the Initial  Fixed Price to the lower of (A) 80% of the lowest
     Variable  Price  during  the  period  beginning  on the date  the  offer is
     announced  and ending on the date the offer is  consummated,  abandoned  or
     terminated or (B) the Initial Fixed Price then in effect, and

     (z) pay a penalty  of 1% per day of the stated  value of $10,000  per share
     plus the  accretion of 4% per annum for a maximum of 10 days in any 365-day
     period.

*    If we complete a sale of all or substantially  all of our assets,  then the
     holders of the Series F Stock may  require us to redeem  their  shares at a
     price per share equal to the greater of

     (1) 125% of the stated value of $10,000 per share plus the  accretion of 4%
     per annum, and

     (2) the value of our common stock that would be issuable upon conversion of
     the Series F Stock.

*    If the  registration  statement  ceases  to be  available  to  the  selling
     stockholders for the resale of their shares in accordance with the terms of
     the registration  rights agreement for more than 10 consecutive  days, then
     the holders of the Series F Stock may require us to redeem  their shares at
     a price per share equal to the greater of

     (1) 125% of the stated value of $10,000 per share plus the  accretion of 4%
     per annum, and

     (2) the value of our common stock that would be issuable upon conversion of
     the Series F Stock.

          However, if the unavailability of the registration  statement does not
     result  from  our  failure  to  use  our  best   efforts  to  maintain  the
     effectiveness of the registration statement and we have not taken voluntary
     action,  or  voluntarily  failed  to take  action,  which  has  caused  the
     registration statement to lapse or become unavailable, then, if the holders
     exercise their redemption rights, we may, in lieu of redemption,

     (y) pay a penalty  of 1% per day of the stated  value of $10,000  per share
     plus the  accretion of 4% per annum for a maximum of 15 days in any 365-day
     period, and

     (z) readjust the Initial  Fixed Price to the lower of (A) 80% of the lowest
     Variable  Price during the period  commencing  on the day the  registration
     statement  became  unavailable  and  ending  on the  day  the  registration
     statement is again  available  for use and (B) the Initial Fixed Price then
     in effect

*    If our common  stock is  delisted  or  suspended  from the Nasdaq  National
     Market for a period of five or more  consecutive  days,  then the holder of
     the  Series F Stock may  require us to redeem  their  shares at a price per
     share equal to the greater of

     (1) 125% of the stated value of $10,000 per share plus the  accretion of 4%
     per annum, and

     (2) the value of our common stock that would be issuable upon conversion of
     the Series F Stock.

          However,  if we have used our best efforts to maintain the listing and
     have not taken any voluntary action,  or voluntarily  failed to take action
     which resulted in a delisting or suspension,  then, if the holders exercise
     their redemption rights, we may, in lieu of redemption,

     (y) readjust the Initial  Fixed Price to 68% of the lower of (A) the lowest
     Variable  Price during the period  commencing  on the date of delisting and
     continuing for 45 trading days thereafter and (B) the Initial


                                       15
<PAGE>

     Fixed Price then in effect, or

     (z) pay a penalty  of 1% per day of the stated  value of $10,000  per share
     plus the  accretion of 4% per annum for a maximum of 15 days in any 365-day
     period.


     In certain cases, if the events described above occur more than once in any
365-day period, there will be a further downward adjustment of the Initial Fixed
Price.

     Pursuant to our agreement with the selling stockholders,  in March 1999, we
held a  special  meeting  of  stockholders  at which  meeting  our  stockholders
approved  the  issuance of any shares upon  conversion  of the Series F Stock in
excess of 20% of the  number of shares  of common  stock we had  outstanding  on
December 9, 1998 (i.e.,  7,577,617) in accordance with the rules and regulations
of The Nasdaq Stock Market, Inc.

     Each  selling  stockholder  has agreed  that if it  engages in short  sales
transactions or other hedging  activities during the 45 trading days immediately
preceding a conversion date which involve,  among other things,  sales of shares
of our common  stock,  the  selling  stockholder  will place its sale orders for
common stock in the course of these  activities  so as not to complete or effect
any sale on any trading day during the period at a price which is lower than the
lowest sale effected on that day by persons  other than the selling  stockholder
and its affiliates.

     Because the market price of our common stock is subject to fluctuation,  we
had  agreed,  pursuant  to the  terms of a  registration  rights  agreement,  to
register for resale by the selling  stockholders  at least 200% of the number of
shares of common  stock  that would be  issuable  if all the Series F Stock were
converted as of the date of filing of the original  registration  statement and,
thereafter,  maintain the  registration of at least 150% of the number of shares
of common  stock  that  would be  issuable  if all the  Series F Stock were then
converted.  Accordingly,  when we originally filed our registration statement in
December 1998, the prospectus  covered  10,000,000 shares of common stock, which
was our good faith estimate of this obligation at that time. As the registration
statement became  insufficient to permit the resale by the selling  stockholders
of all the common  shares  issuable upon  conversion of the Series F Stock,  the
selling  stockholders,  in addition to any other remedies,  claimed they had the
right to require us to redeem all or any  portion of the  remaining  outstanding
shares of Series F Stock (at a price  equal to the greater of 125% of the stated
value of $10,000 per share plus the  accretion  of 4% per annum and the value of
the Common Stock which would have been issued upon conversion) as well as pay to
them a penalty of $5 per share of Series F Stock  with  respect to each day that
the registration statement was insufficient.

     We had  received  a  waiver,  dated  October  11,  1999,  from the  selling
stockholders  with  respect  to the  rights  discussed  above  either to require
redemption  or  to  receive   penalties   conditioned  upon  our  (a)  filing  a
registration  statement,  on or before November 11, 1999, covering at least 200%
of the number of shares of common stock that would be issuable if all the Series
F Stock  were  converted  as of the  date  of the  filing  of this  registration
statement and (b) having this registration  statement  declared  effective on or
before December 11, 1999.

     Subject to our satisfying certain conditions, we have the right (a) upon 20
days advanced notice, to redeem all of the outstanding  shares of Series F Stock
at a 20% annualized premium, (b) upon three days advanced notice, to require the
selling stockholders to convert their Series F Stock if the closing bid price of
our common stock  exceeds  $5.00 for a specified  period of time.  We would have
lost  these  rights  if we had  failed  to file the  registration  statement  by
November  11,  1999  or  failed  to use our  best  efforts  to have it  declared
effective by December  11,  1999,  and (c) upon five days  advanced  notice,  to
redeem  any or all  shares  of  Series F Stock  presented  for  conversion  at a
conversion  price of less than $1.80 at a redemption  price equal to 105% of the
stated value of $10,000 per share plus the accretion of 4% per annum.

     While this registration  statement covers an additional 9,878,463 shares of
our common stock in addition to the 5,316,983 shares of common stock included in
our prior prospectus, we would not be required to issue any shares which are the
subject of this additional  registration  statement unless the Variable Price at
the time of conversion on average is below $1.40 (increased over time due to the
4% accretion to the stated value).  See "Selling  Stockholders"  for information
concerning the number of shares that are currently issuable.

     If we were required to redeem the Series F Stock or make any of the penalty
payments, we may not have the financial ability to make these payments.  Even if
we did  have the  financial  ability  to  redeem  the  Series F Stock or pay the
required  penalties,  any payments could  significantly and adversely affect our
financial


                                       16
<PAGE>

condition and deplete its cash resources.

     In connection  with our agreement  with the selling  stockholders,  we have
agreed to  reimburse  them for up to $50,000 of their  legal  expenses  they had
incurred in connection with the issuance of the Series F Stock.

     On November 24, 1999,  we entered  into an agreement  with HFTP  Investment
L.L.C.  relating to the shares of Series F Stock  currently held by it. Pursuant
to this agreement,  (a) we honored HFTP Investment's conversion of 105 shares of
Series F Stock  into  924,614  shares of our common  stock,  and (b) we have the
right to redeem any or all of its remaining 445 shares of Series F Stock, at any
time on or before December 15, 1999, at a redemption price that varies from 107%
to 109% of the $10,000  stated amount per preferred  share,  depending upon when
during this period we redeem.  We are under no obligation to redeem these shares
either before or after  December 15, 1999.  HFTP  Investment  has agreed that it
will not convert any additional  Series F Stock on or before  December 15, 1999,
and will not  increase  its net short  position in our common stock on or before
that date. We are seeking to conclude similar  agreements with the other selling
stockholders.  We  also  are  pursuing  negotiations  to  obtain  the  financing
necessary to effect the  redemptions.  We cannot assure you that will be able to
enter into satisfactory arrangements, or any arrangements at all, with the other
investors  or with any  financing  source  in order to be able to  complete  any
redemptions. Even if we do, we may determine not to complete any redemption.

                                Use of Proceeds

     We will not receive any  proceeds  from the sale of our common stock by the
selling  stockholders.  However,  we did receive net  proceeds of  approximately
$12,330,000 from the issuance of the Series F Stock to the selling  stockholders
in December 1998.

     We intend to continue to use these proceeds for general corporate purposes,
including  research  and  development,   clinical  trials,  regulatory  filings,
manufacturing,  marketing  and  sales,  general  and  administrative  and  other
expenses, acquisitions of products and technologies, license, milestone, royalty
and similar payments, and strategic and other acquisitions.


                              Selling Stockholders

     The table  below  presents  the  following  information:  (1) the number of
shares of Series F Stock  owned by each  selling  stockholder  as of the date of
this prospectus,  (2) the number of shares of common stock beneficially owned by
each selling  stockholder as of the date of this  prospectus,  (3) the number of
shares that the selling  stockholder is offering under this prospectus,  and (4)
the number of shares that the selling  stockholder  will  beneficially own after
the completion of this offering.

     Except as otherwise noted in the table, the number and percentage of shares
beneficially  owned by each selling  stockholder is determined as of the date of
this  prospectus in accordance  with Rule 13d-3 of the Securities  Exchange Act,
and the  information is not necessarily  indicative of beneficial  ownership for
any other purpose.  Under this rule, beneficial ownership includes any shares as
to which the selling  stockholder  has sole or shared voting power or investment
power and also any shares which the selling stockholder has the right to acquire
within 60 days of the date of this  prospectus  through  the  conversion  of the
Series F Stock or the  exercise  of any  stock  option  or other  right.  Unless
otherwise indicated in the footnotes, each person has sole voting and investment
power with respect to the shares shown as beneficially owned.

     The number of shares of our common  stock  shown as  beneficially  owned by
each selling  stockholder prior to the offering and the number of shares offered
by each selling stockholder represents shares of our common stock issuable to it
assuming  conversion,  as of December  6, 1999,  of all shares of Series F Stock
owned by that selling  stockholder  with respect to the $10,000  stated value of
the Series F Stock plus an  accretion  of 4% per year.  The number of shares was
calculated  using an assumed  conversion  price of $1.18,  which  represents the
average of the 15 lowest  closing bid prices for our common  stock during the 45
consecutive trading days ending on December 3, 1999. As described in the section
"Immunomedics - December 1998 Financing"  above,  the actual number of shares of
our common stock  issuable  upon  conversion of the Series F Stock is based upon
the market price of common stock at the time of conversion.  In accordance  with
the provisions of the Series F Stock,  the conversion  price will fluctuate from
time to  time  based  on  changes  in the  market  price  of our  common  stock.
Therefore,  the actual  number of shares of common  stock may be less or greater
than  the  number  of  shares  shown  as  beneficially   owned  by  the  selling
stockholders or the number of


                                       17
<PAGE>

shares offered by this prospectus.  Under the certificate of designation for the
Series F Stock, no selling  stockholder can convert Series F Stock to the extent
that the conversion would cause the selling  stockholder's  beneficial ownership
of our  common  stock  to  exceed  4.99% of our  outstanding  common  stock,  or
2,124,298  shares at December 6, 1999. In  calculating  a selling  stockholder's
beneficial ownership for this purpose, the selling stockholder would exclude any
shares which it would be considered  to  beneficially  own through  ownership of
unconverted Series F Stock.

     The number of shares that will  ultimately be issued upon conversion of the
Series F Stock is dependent, subject to certain limitations, upon the average of
certain  closing bid prices of our common stock prior to conversion as discussed
above.  Accordingly,  the number of shares  that may be issued and the number of
shares  offered  hereby  cannot be  determined  at this  time.  As a result,  as
discussed  above,  we have  agreed to  register  for resale at least 200% of the
number of shares of common  stock  that  would be  issuable  if all the Series F
Stock were converted as of the date of the filing of the registration  statement
of which this  prospectus  is a part. As of December 6, 1999, we would have been
required to issue  approximately  6,335,014  shares of our common  stock had the
holders  converted all of their 718.5 remaining  outstanding  shares of Series F
Stock on this date.  As discussed  above,  we have agreed to register a total of
15,821,153 shares of our common stock. Accordingly, the selling stockholders may
be entitled to sell approximately  8,860,432  additional shares pursuant to this
prospectus,  if these shares are issued to them in accordance  with the terms of
the Series F Stock.

     The  number of shares  shown as being  beneficially  owned by each  selling
stockholder after the offering assumes that the selling stockholder has sold all
the shares of our common stock which may be sold pursuant to this prospectus.

     None of the selling  stockholders has had a material  relationship  with us
within the past three years,  other than as a result of their purchase of shares
of our Series F Stock. As of December 6, 1999, no selling  stockholder owned any
shares  of our  common  stock  other  than  the  shares  they may  acquire  upon
conversion of the Series F Stock,  other than Fisher Capital Ltd. which directly
owned  425,834  shares of our common  stock,  and  Wingate  Capital  Ltd.  which
directly owned 26,310 shares of our common stock.

<TABLE>
<CAPTION>

                                                                      Shares of                             Shares of
                                                     Shares of       Common Stock                          Common Stock
                                                     Preferred       Beneficially        Shares of         Beneficially
                                                       Stock        Owned Prior to      Common Stock       Owned After
Selling Stockholder                                    Owned         the Offering      Being Offered         Offering
<S>                                                  <C>            <C>                <C>                 <C>
AG Super Fund International Partners,
L.P.(1)                                                    13.0          114,621            114,621                  0
Fisher Capital Ltd.(2)                                     80.0        1,131,194            705,360            425,834
GAM Arbitrage investments, Inc.(1)                         12.0          105,804            105,804                  0
HFTP Investment L.L.C.(3)                                 445.0        3,923,565          3,923,565                  0
Leonardo, L.P.(1)                                          84.5          745,036            745,036                  0
Ramius Fund, Ltd.(1)                                       27.0          238,059            238,059                  0
Raphael, L.P.(1)                                           14.0          123,438            123,438                  0
Wingate Capital Ltd.(2)                                    43.0          405,441            379,131             26,310
- ----------------
</TABLE>

(1)  Angelo, Gordon & Co., L.P. is a general partner of Leonardo, L.P., AG Super
     Fund  International  Partners,  L.P. and Raphael,  L.P.,  and is investment
     advisor to GAM  Arbitrage  Investments,  Inc.  and Ramius  Fund,  Ltd.  and
     consequently  has voting control and investment  discretion over securities
     held by these  entities.  The ownership for each of these entities does not
     include the ownership information for the other entities.  Angelo, Gordon &
     Co.,  L.P.  and  each  of  the  referenced  entities  disclaims  beneficial
     ownership of any of our securities held by the other  referenced  entities.
     Mr. John M. Angelo,  the Chief Executive  Officer of Angelo,  Gordon & Co.,
     L.P., and Mr.  Michael R. Gordon,  the Chief  Operating  Officer of Angelo,
     Gordon & Co.,  L.P.,  are the sole general  partners of AG Partners,  L.P.,
     which is the sole  general  partner of Angelo,  Gordon & Co.,  L.P. In this
     capacity, Messrs. Angelo and Gordon may be


                                       18
<PAGE>

     deemed  to be the  beneficial  owner  of any our  securities  deemed  to be
     beneficially owned by Angelo,  Gordon & Co., L.P. However,  Messrs.  Angelo
     and Gordon disclaim beneficial ownership of these securities.

(2)  Citadel Limited  Partnership is the trading manager of Wingate Capital Ltd.
     and Fisher Capital Ltd. and  consequently has voting control and investment
     discretion  over  securities  held  by  these  entities.   Citadel  Limited
     Partnership  is  indirectly  controlled  by Mr.  Kenneth  C.  Griffin.  The
     ownership  for each  referenced  entity  does  not  include  the  ownership
     information for the other referenced  entity.  Citadel Limited  Partnership
     and each of the referenced entities disclaims  beneficial  ownership of any
     of our securities held by the other entities.  Mr. Griffin may be deemed to
     be the beneficial ownership of any of our securities  beneficially owned by
     Citadel  Limited  Partnership  or the  referenced  entities.  However,  Mr.
     Griffin disclaims beneficial ownership of these securities.

(3)  Promethean  Investment  Group  L.L.C.  is the  investment  advisor for HFTP
     Investment  L.L.C.  and  consequently  has voting  control  and  investment
     discretion over securities held by this entity. Promethean Investment Group
     L.L.C.  is indirectly  controlled by Mr. James F. O'Brien,  Jr.  Promethean
     Investment  Group  L.L.C.  disclaims  beneficial  ownership  of  any of our
     securities held by HFTP Investment  L.L.C.  Mr. O'Brien may be deemed to be
     the  beneficial  ownership of any of our securities  beneficially  owned by
     Promethean  Investment Group L.L.C. or HFTP Investments L.L.C. However, Mr.
     O'Brien disclaims beneficial ownership of these securities.  As a result of
     the limitation  discussed  above in this section,  the selling  stockholder
     would be prevented  from  converting  Series F Stock to the extent that the
     conversion would cause the selling  stockholder's  beneficial  ownership of
     our common stock to exceed 4.99% of our outstanding common stock.


                              Plan of Distribution

Manner of Sales; Broker-Dealer Compensation.

     The  selling  stockholders,  or any  successors  in interest to the selling
stockholders,  may sell any shares of common  stock that they  acquire when they
convert  shares of Series F Stock.  The sale of our common stock may be effected
in one or more of the following methods:

*    ordinary brokers' transactions;

*    transactions  involving  cross or block  trades or  otherwise on the Nasdaq
     National Market;

*    purchases by brokers,  dealers or  underwriters  as principal and resale by
     these purchasers for their own accounts pursuant to this prospectus;

*    "at the market" to or through market makers or into an existing  market for
     our common stock;

*    in other ways not involving  market makers or established  trading markets,
     including direct sales to purchases or sales effected through agents;

*    through  transactions  in  options,  swaps  or other  derivatives  (whether
     exchange-listed or otherwise);

*    in privately negotiated transactions;

*    to cover short sales; or

*    any combination of the foregoing.

     The selling stockholders also may sell the shares in reliance upon Rule 144
under the  Securities  Act at such times as they are  eligible to do so. We have
been  advised  by  the  selling   stockholders  that  they  have  not  made  any
arrangements  for the  distribution  of the  shares  of common  stock.  Brokers,
dealers  or  underwriters  who effect  sales for the  selling  stockholders  may
arrange for other brokers,  dealers or  underwriters  to  participate.  Brokers,
dealers  or  underwriters  engaged  by the  selling  stockholders  will  receive
commissions or


                                       19
<PAGE>

discounts  from  them in  amounts  to be  negotiated  prior to the  sale.  These
brokers, dealers or underwriters may act as agent or as principals.

     From time to time,  one or more of the  selling  stockholders  may  pledge,
hypothecate or grant a security  interest in some or all of the shares of common
stock acquired by them upon conversion of the Series F Stock,  and the pledgees,
secured  parties or persons to whom these  securities  have been pledged  shall,
upon foreclosure in the event of default,  be considered a selling  stockholders
hereunder.  In addition,  subject to the limitations  discussed above, a selling
stockholder  may,  from time to time,  sell  short our  common  stock.  In these
instances, this prospectus may be delivered in connection with these short sales
and the shares of our common stock issued upon  conversion of Series F Stock may
be used to cover these short sales.

     From time to time one or more of the  selling  stockholders  may  transfer,
pledge,  donate or assign  shares of our  common  stock  that it  acquired  upon
conversion of Series F Stock to lenders or others and each of these persons will
be considered a selling stockholder for purposes of this prospectus.  The number
of shares of our common stock beneficially  owned by those selling  stockholders
who so  transfer,  pledge,  donate or assign  shares of our  common  stock  will
decrease as and when they take these actions.  The plan of distribution  for our
common stock by the selling stockholders' set forth herein will otherwise remain
unchanged,  except that the  transferees,  pledgees,  donees or other successors
will be considered selling stockholders hereunder.

     Subject to the limitations discussed above, a selling stockholder may enter
into hedging  transactions with broker-dealers and the broker-dealers may engage
in short sales of our common stock in the course of hedging the  positions  they
assume with this selling stockholder, including in connection with distributions
of our common  stock by these  broker-dealers.  A selling  stockholder  may also
enter into option or other  transactions  with  broker-dealers  that involve the
delivery  of our  common  stock to the  broker-dealers,  who may then  resell or
otherwise  transfer these shares. A selling  stockholder also may loan or pledge
our common stock to a broker-dealer  and the  broker-dealer  may sell our common
stock so loaned or upon a default  may sell or  otherwise  transfer  the pledged
common stock.

Filing of a Post-Effective Amendment In Certain Instances.

     If any selling stockholder  notifies us that it has entered into a material
arrangement  (other than a customary  brokerage account agreement) with a broker
or dealer for the sale of shares of common stock under this prospectus through a
block trade, purchase by a broker or dealer or similar transaction, we will file
a post- effective  amendment to the registration  statement under the Securities
Act. The post-effective amendment will disclose:

*    The name of each broker-dealer involved in the transaction.

*    The number of shares of common stock involved.

* The price at which those shares of common stock were sold.

*    The   commissions   paid  or  discounts  or  concessions   allowed  to  the
     broker-dealer(s).

*    If   applicable,   that  these   broker-dealer(s)   did  not   conduct  any
     investigation  to verify  the  information  contained  or  incorporated  by
     reference in this prospectus, as supplemented.

*    Any other facts material to the transaction.

Certain Persons May Be Deemed to Be Underwriters

     The selling  stockholders and any broker-dealers who execute sales for them
may be deemed to be  "underwriters"  within the  meaning of the  Securities  Act
because  of the  number of shares of common  stock to be sold or resold by these
persons or entities or the manner of sale of these shares, or both. If a selling
stockholder  or  any  broker-dealer  or  other  holders  were  determined  to be
underwriters,  any discounts,  concessions or commissions received by them or by
brokers or dealers  acting on their  behalf and any profits  received by them on
the resale of their  shares of common  stock might be deemed to be  underwriting
discounts and commissions under the Securities Act.

Regulation M


                                       20
<PAGE>

     We have  informed the selling  stockholders  that  Regulation M promulgated
under the Securities  Exchange Act may be applicable to them with respect to any
purchase or sale our common  stock.  In  general,  Rule 102 under  Regulation  M
prohibits  any person  connected  with a  distribution  of our common stock from
directly or indirectly  bidding for, or  purchasing  for any account in which it
has a beneficial interest,  any of our common stock or any right to purchase our
common  stock,  for a period of one business day before and after  completion of
its participation in the distribution.

     During  any  distribution  period,   Regulation  M  prohibits  the  selling
stockholders and any other persons engaged in the distribution  from engaging in
any  stabilizing  bid or  purchasing  our common stock except for the purpose of
preventing  or retarding a decline in the open market price of our common stock.
None of these persons may effect any  stabilizing  transaction to facilitate any
offering  at the market.  As the selling  stockholders  will be  reoffering  and
reselling  our common stock at the market,  Regulation M will prohibit them from
effecting any  stabilizing  transaction  in  contravention  of Regulation M with
respect to our common stock.

Indemnification and Other Matters

     We paid all of the expenses incident to the registration, offering and sale
of our  common  stock by the  selling  stockholders  to the  public  other  than
commissions or discounts of underwriters, broker-dealers or agents. We also have
agreed to  indemnify  certain of the selling  stockholders  and certain  related
persons against certain liabilities,  including liabilities under the Securities
Act. Insofar as indemnification for liabilities arising under the Securities Act
may be permitted to our directors,  officers and  controlling  persons,  we have
been  advised that in the opinion of the SEC this  indemnification  agreement is
against  public  policy as expressed in the  Securities  Act and is,  therefore,
unenforceable.

     This  offering  will  terminate on the earlier of (a) the date on which the
shares are eligible for resale without restriction pursuant to Rule 144(k) under
the  Securities Act or (b) the date on which all shares offered hereby have been
sold by the selling stockholders.


                                  Legal Matters

     Warshaw Burstein Cohen  Schlesinger & Kuh, LLP will give its opinion on the
validity  of the  common  stock.  As of the  date  of this  prospectus,  certain
partners of this firm  beneficially  own an  aggregate of 1,200 shares of common
stock.


                                     Experts

     Our consolidated financial statements as of June 30, 1999 and 1998, and for
each of the  years in the  three-year  period  ended  June 30,  1999  have  been
incorporated by reference herein and in the  registration  statement in reliance
upon  the  report  of  KPMG  LLP,  independent   certified  public  accountants,
incorporated by reference herein, and upon the authority of said firm as experts
in accounting and auditing.


                                       21
<PAGE>


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