CYTOGEN CORP
S-3, 2000-04-11
IN VITRO & IN VIVO DIAGNOSTIC SUBSTANCES
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     As filed with the Securities and Exchange Commission on April 11, 2000.
                                                           Registration No. 333-
================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                              Washington, DC 20549
                               -------------------
                                    FORM S-3
                             REGISTRATION STATEMENT
                                     Under
                           THE SECURITIES ACT OF 1933
                               ------------------
                              CYTOGEN CORPORATION
             (Exact name of registrant as specified in its charter)

          Delaware                                               22-2322400
(State or other jurisdiction                                   (I.R.S. Employer
of incorporation or organization)                            Identification No.)

                         600 College Road East CN 5308
                        Princeton, New Jersey 08540-5308
                                 (609) 750-8200
(Address,  including zip code,  and telephone  number,  including  area code, of
                   registrant's principal executive offices)
                           Donald F. Crane, Jr. Esq.
                       Vice President and General Counsel
                              Cytogen Corporation
                         600 College Road East CN 5308
                       Princeton, NJ 08540 (609) 750-8200
(Name, address including zip code, and telephone number, including area code, of
                               agent for service)
                               ------------------
                                   Copies to:
                            James J. Marino, Esquire
                             Dechert Price & Rhoads
                     997 Lenox Drive, Building 3, Suite 210
                        Lawrenceville, New Jersey 08648
                               ------------------

     Approximate date of commencement of proposed sale to the public:  From time
to time after the effective  date of this  Registration  Statement.

     If the only  securities  being  registered  on this Form are to be  offered
pursuant to dividend or interest  reinvestment plans, please check the following
box.
    ---
     If any of the securities being registered on this Form are to be offered on
a delayed or continuous  basis  pursuant to Rule 415 under the Securities Act of
1933, as amended, other than securities offered only in connection with dividend
or interest reinvestment plans, check the following box. X
                                                        ---
     If this Form is filed to  register  additional  securities  for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective  registration  statement  for the same  offering.
                                                           ---
     If this Form is a  post-effective  amendment  filed pursuant to Rule 462(c)
under the  Securities  Act,  check the following box and list the Securities Act
registration  statement number of the earlier effective  registration  statement
for the same  offering.
                       ---
     If delivery of the  prospectus is expected to be made pursuant to Rule 434,
please check the following box.
                               ---
<TABLE>
<CAPTION>
                                        CALCULATION OF REGISTRATION FEE
=====================================================================================================================
                                                           Proposed maximum      Proposed maximum
  Title of each class of                   Amount to be        offering         aggregate offering       Amount of
securities to be registered                 registered      price per unit(1)          price         registration fee
- ---------------------------------------------------------------------------------------------------------------------
<S>                                         <C>                 <C>                 <C>                   <C>
Common Stock, par value $.01 per share      1,086,394           $8.53               $9,268,570            $2,577
- ---------------------------------------------------------------------------------------------------------------------
</TABLE>

(1)  Estimated solely for the purpose of computing the registration fee required
     by Section 6(b) of the Securities Act and computed  pursuant to Rule 457(c)
     under the  Securities Act based upon the average of the high and low prices
     of the Common Stock on April 7, 2000,  as reported on the Nasdaq  National
     Market.
                               ------------------
The Registrant hereby amends this  Registration  Statement on such date or dates
as may be necessary to delay its effective date until the Registrant  shall file
a further amendment which specifically  states that this Registration  Statement
shall  thereafter  become  effective  in  accordance  with  Section  8(a) of the
Securities Act or until the  Registration  Statement  shall become  effective on
such date as the Securities  and Exchange  Commission,  acting  pursuant to said
Section 8(a), may determine.

================================================================================
<PAGE>

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
The  information  in this  prospectus in not complete and may be changed.  These
securities  may not be sold  until the  registration  statement  filed  with the
Securities and Exchange Commission is effective. This prospectus in not an offer
to sell these  securities and is not soliciting an offer to buy these securities
in any state where the offer or sale is not permitted.
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++


PROSPECTUS                           Subject to Completion, dated April __, 2000
- --------------------------------------------------------------------------------

                              CYTOGEN CORPORATION

                        1,086,394 Shares of Common Stock

We are  registering  our  common  stock for resale by the  selling  stockholders
identified in this prospectus.  We will not receive any of the proceeds from the
sale of shares by the selling  stockholders.  Our common  stock is listed on the
Nasdaq  National  Market  under the symbol  "CYTO."  On April 7, 2000,  the last
reported sales price for our common stock was $8.19 per share.

Investing  in our  common  stock  involves  a high  degree of risk.  You  should
carefully  consider certain "Risk factors" in determining  whether to buy any of
our common stock. See page 2.

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.

                  The date of this prospectus is April , 2000.
<PAGE>

                              CYTOGEN CORPORATION

     Cytogen is an  established  biopharmaceutical  company  with two  principal
lines of business,  proteomics  and oncology.  We are extending our expertise in
antibodies and molecular  recognition  to the  development of new products and a
proteomics-driven  drug discovery  platform.  We have  established a pipeline of
product  candidates  based upon our proprietary  antibody and prostate  specific
membrane antigen,  or PSMA,  technologies.  We are also developing a proprietary
protein  pathway  database  as a drug  discovery  and  development  tool for the
pharmaceutical and biotechnology industries.

     Our  cancer  management   franchise   currently  comprises  three  marketed
FDA-approved  products:  ProstaScint,  used to image the  extent  and  spread of
prostate  cancer;  OncoScint CR/OV,  marketed as a diagnostic  imaging agent for
colorectal  and  ovarian  cancer  and  Quadramet,  marketed  for the  relief  of
cancer-related  bone pain. We are  extending  our cancer  pipeline by exploiting
PSMA,  which we  exclusively  licensed from  Memorial  Sloan-  Kettering  Cancer
Center.  PSMA is a unique antigen highly  expressed in prostate cancer cells and
in the neovasculature of a variety of other solid tumors, including breast, lung
and colon.  We are  developing  our PSMA  technology  as part of our approach to
offering  a full range of  prostate  cancer  management  products  and  services
throughout the progression of the disease,  including  gene-based  immunotherapy
vaccines,   antibody-delivered   therapeutic  compounds  and  novel  assays  for
detection of primary prostate cancer. We also plan to apply our PSMA technology,
including  therapeutics and in vitro  diagnostics,  toward other types of cancer
based upon our  experience  in prostate  cancer.  Our in vivo  immunotherapeutic
development   program  is  being  conducted  in  collaboration   with  Progenics
Pharmaceuticals, Inc.

     Proteomics  is the study of the  expression  and  interaction  of proteins.
Genomics is the study and identification of an organism's genetic makeup.  While
genomics provides  important  information  regarding genetic makeup, it does not
directly   provide   information   regarding   protein   functions   or  protein
interactions.  However, genomics data can prove useful in proteomics research as
a source of obtaining  complete protein sequences of ligands we have identified.
Public   availability  of  this  genomics   information   allows  for  effective
integration in our database of public and proprietary information. We recognized
in our past research that the key to  understanding  or developing  the means to
intervene in diseases was primarily based on understanding  protein interactions
rather  than  only  through  the use or study of  genomics.  We  undertook  this
approach on our own initiative and with our own funds.  Our proteomics  program,
under development by our subsidiary,  AxCell Biosciences Corporation, is focused
on the identification of protein interaction and signaling pathways within cells
as relating to disease processes.

     We  utilize  our  proprietary   proteomics   technology  to  map  selective
protein-protein   interactions   and  to   develop  a   database,   called   the
Inter-Functional  Proteomic  Database,  or IFP  Database,  which  includes  data
relating  to  protein   signaling   pathways   linked  to  a  variety  of  other
bioinformatic  data.  The IFP  Database  is  designed  to  permit  customers  to
integrate existing databases, both public and proprietary,  with our proprietary
data to create a `virtual  laboratory'  on the computer  desktop of  researchers
involved in drug discovery.  We believe this database has significant  potential
commercial value to the pharmaceutical  and biotechnology  industries as a means
of expediting drug target  identification,  validation,  screen  development and
lead compound  optimization faster and cheaper than with current  methodologies.
These proprietary  technologies are designed to provide a platform from which we
can quickly and  cost-effectively  determine  protein-protein  interactions  and
build pathways of  intracellular  signaling data. Our IFP Database also offers a
consolidated platform to enable statistical and mathematical modeling of complex
protein pathways.

     Our  executive  offices  are  located  at 600  College  Road  East CN 5308,
Princeton, New Jersey 08540-5308, and our telephone number is (609) 750-8200.

<PAGE>


                                  RISK FACTORS

     You should  carefully  consider the risks described below together with all
of  the  other  information  included  or  incorporated  by  reference  in  this
prospectus before making an investment  decision.  If any of the following risks
occurs,  our business,  financial  condition or results of  operations  could be
harmed.  In that case, the trading price of our common stock could decline,  and
you may lose all or part of your  investment.  We have a  history  of  operating
losses and accumulated deficit and expect to incur losses in the future.

We have a history of operating losses since our inception.  We had net income of
$729,000  during the year ended  December 31, 1999 which  included  certain non-
operating gains. We had net losses of $13,152,000 during the year ended December
31, 1998 and  $30,712,000  during the year ended  December 31,  1997.  We had an
accumulated deficit of $301,283,000 as of December 31, 1999. In order to develop
and  commercialize  our  technologies,  particularly our proteomics  program and
prostate specific membrane antigen, or PSMA, technology, and expand our oncology
products, we expect to incur significant increases in our expenses over the next
several years. As a result,  we may continue to report  operating losses for the
near future and we may never be profitable or achieve significant revenues.

Our ability to achieve  significant  revenues or profitability  will depend upon
numerous factors, including:

- -    successful product development;

- -    our ability to acquire,  develop and commercialize  complementary  products
     and technologies; and

- -    our ability to achieve  increased sales for our existing products and sales
     for any new products.

We  are  in  the  early  stages  of  development  and  commercialization  of our
technology platforms and may never achieve the goals of our business plan.

Early last year, we completed our  restructuring  to focus on development of our
prostate specific membrane antigen, or PSMA, and proteomics technologies and the
marketing of our existing products. We may be unable to continue to successfully
develop or commercialize these technologies.  Our PSMA and proteomics technology
are still in the early stages of  development.  We have only  recently  begun to
incorporate our proteomics technology into commercialized products.

We began operations in 1980 and have been engaged primarily in research directed
toward the development,  commercialization  and marketing of products to improve
diagnosis  and  treatment  of cancer and other  disease.  In December  1992,  we
introduced for commercial use our OncoScint  imaging agent.  In October 1996, we
introduced for commercial use our  ProstaScint  imaging agent. In March 1997, we
introduced for commercial use our Quadramet therapeutic product.  These products
have not yet  achieved  significant  commercial  success.  In  1998,  we began a
restructuring  of our  company  to  focus  on the  development  of our  PSMA and
proteomics technologies and marketing of these existing products.

Our business is therefore subject to the risks inherent in the development of an
early stage business enterprise, such as the need:

- -    to obtain  sufficient  capital to support the  expenses of  developing  our
     technology and commercializing our products;

- -    to ensure that our products are safe and effective;

- -    to  manufacture  our products in sufficient  quantities and at a reasonable
     cost;

- -    to develop a sufficient market for our products; and

- -    to attract and retain qualified management, sales, technical and scientific
     staff.


                                      -2-
<PAGE>

The problems  frequently  encountered  using new technologies and operating in a
competitive  environment  also may affect our  business.  If we fail to properly
address these risks and attain our business objectives, our business, results of
operations and financial condition will suffer.

Our proteomics program is at an early stage of development.

We have developed and intend to continue to develop our proteomics program. This
technology  involves  new  approaches  and remains  commercially  unproven.  Our
technology  and  development  focus is  primarily  directed  toward  offering an
infrastructure  to companies for the  development of drugs to treat a variety of
complex human diseases. There is limited understanding generally relating to the
role of proteins in  diseases,  and few  products  based on protein  interaction
discoveries  have been  developed  and  commercialized.  Even if our  proteomics
program was successful in identifying and validating  biological targets,  there
is no  guarantee  that our  customers  will be able to develop or  commercialize
products to improve human health.

In  addition,  the  success of our  proteomics  technology  will depend upon our
ability to use software  tools to generate data that relates  protein  signaling
pathways  to a  variety  of  other  bioinformatic  information.  Because  of the
complexity  of this  data,  we may not be able to detect  and  remedy any design
defects or software  errors in our  existing or future  technologies,  including
databases.

Due to the  specialized  nature  and  price  of our  proteomics  technology  and
services,  there  are a  limited  number  of  pharmaceutical  and  biotechnology
companies that are potential customers.  Additional reasons why there may not be
a great demand for our proteomics technology and services include:

- -    our potential customers may determine to conduct in-house research;

- -    our competitors may offer similar services at competitive prices;

- -    we may not be able to service  satisfactorily the needs of our potential or
     actual customers;

- -    others may publicly disclose or patent proprietary information contained in
     our IFP  Database  (including  information  related  to  protein  signaling
     pathways  or  target  candidates)  or  relating  to  prostate  antigens  or
     antibodies; and

- -    technological  innovations  may be  discovered  that are more advanced than
     those used by or available to us.

Our  technology  program  for  proteomics  is  still  in  the  early  stages  of
development.  We may not be able to populate our IFP Database  with  information
that is useful to potential  customers in a timely  manner.  Even if we complete
and develop  successfully our proteomics  technology,  the technology may not be
accepted by, or be useful to, our customers.

Our PSMA  product  development  program is novel and,  consequently,  inherently
risky.

We are subject to the risks of failure  inherent in the  development  of product
candidates based on new technologies, including our PSMA technology. These risks
include the possibility that:

- -    the technologies we use will not be effective;

- -    our  product  candidates  will be unsafe or  otherwise  fail to receive the
     necessary regulatory approvals;

- -    our product candidates will be hard to manufacture on a large scale or will
     be uneconomical to market; and

- -    we will not successfully overcome technological challenges presented by our
     products.

Our  objectives  include  developing  our  PSMA  technology  into  novel  cancer
therapeutics,   including  a  cancer  vaccine.

                                      -3-
<PAGE>
To our knowledge, no cancer therapeutic vaccine has been approved for marketing.
Our other research and development  programs involve  similarly novel approaches
to human  therapeutics.  Consequently,  there is no precedent for the successful
commercialization  of therapeutic  products based on our PSMA  technologies.  We
cannot assure you that any of our products will be successfully developed.

We are heavily  dependent on market  acceptance of ProstaScint and Quadramet for
near-term revenues.

ProstaScint  and Quadramet are expected to account for a significant  percentage
of our product-related  revenues in the near future. For the year ended December
31, 1999,  revenues from ProstaScint and Quadramet  accounted for  approximately
92% of our product related revenues.

Because these products contribute the majority of our product-related  revenues,
our business,  financial  condition  and results of  operations  depend on their
acceptance as safe, effective and cost-efficient alternatives to other available
treatment and diagnostic protocols by the medical community, including:

- -    health care providers, such as hospitals and physicians; and

- -    third-party  payors,  including  Medicare,   Medicaid,   private  insurance
     carriers and health maintenance organizations.

Our  customers,   including  technologists  and  physicians,  must  successfully
complete our Partners in  Excellence  Program,  or PIE  Program,  a  proprietary
training program designed to promote the correct  acquisition and interpretation
of ProstaScint  images.  This approach is,  therefore,  technique  dependent and
requires a learning  commitment on the part of users.  We cannot assure you that
additional physicians will make this commitment or otherwise accept this product
as part of their treatment practices.

Berlex  Laboratories,  Inc.  markets  Quadramet in the United States  through an
agreement that we entered into in October 1998. We cannot assure you that Berlex
will be able to successfully market Quadramet or that this agreement will result
in  significant  revenues  for us.  We  recently  obtained  marketing  rights to
Quadramet in Canada,  but have not yet implemented a selling program.  We cannot
assure you that Quadramet can be marketed effectively in Canada, or that it will
contribute significantly to our revenues.

We cannot assure you that Quadramet will be approved for additional indications,
due to  uncertainty as to efficacy or safety for other  purposes,  to regulatory
obstacles and to physician preferences for existing or competing practices.

Accordingly,  we cannot assure you that  ProstaScint  or Quadramet  will achieve
market  acceptance on a timely basis,  or at all. If ProstaScint or Quadramet do
not achieve broad market acceptance,  we may not be able to generate  sufficient
product revenue to become profitable.

We may need to raise additional capital which may not be available.

We have incurred  negative cash flows from operations since  inception.  We have
expended, and will need to continue to expend, substantial funds to complete our
planned product development efforts, including our proteomics and PSMA programs.
While we believe that the proceeds from this offering will be sufficient to meet
our development and  commercialization  needs for the  foreseeable  future,  our
future capital  requirements  and the adequacy of our available  funds depend on
many factors, including:

- -    successful commercialization of our products;

- -    acquisition of complementary products and technologies;

- -    magnitude, scope and results of our product development efforts;

- -    progress of preclinical studies and clinical trials;


                                      -4-
<PAGE>

- -    progress of regulatory affairs activities;

- -    costs of filing,  prosecuting,  defending and  enforcing  patent claims and
     other intellectual property rights;

- -    competing technological and market developments; and

- -    expansion of strategic  alliances for the sale,  marketing and distribution
     of our products.

We may raise additional capital through public or private equity offerings, debt
financings or additional  collaborations and licensing arrangements.  Additional
financing may not be available to us when we need it, or, if  available,  we may
not be able to obtain financing on terms favorable to us or our stockholders. If
we raise  additional  capital by issuing  equity  securities,  the issuance will
result in ownership  dilution to our stockholders.  If we raise additional funds
through  collaborations  and  licensing  arrangements,  we  may be  required  to
relinquish  rights to certain of our  technologies  or product  candidates or to
grant licenses on unfavorable  terms. If we relinquish  rights or grant licenses
on  unfavorable  terms,  we may not be able to develop or market  products  in a
manner that is profitable to us. If adequate funds are not available, we may not
be able to conduct research activities,  preclinical studies, clinical trials or
other activities relating to the successful commercialization of our products.

Competition  in our field is intense and likely to increase.  We face,  and will
continue  to  face,  intense  competition  from  one or  more  of the  following
entities:

- -    pharmaceutical companies;

- -    biotechnology companies;

- -    bioinformatics companies;

- -    diagnostic companies;

- -    academic and research institutions; and

- -    government agencies.

All of our  lines of  business  are  subject  to  significant  competition  from
organizations  that are pursuing  technologies and products that are the same as
or similar to our technology and products.  Many of the organizations  competing
with us have greater  capital  resources,  research and  development  staffs and
facilities and marketing capabilities.

We believe  that our future  success will depend in large part on our ability to
maintain a competitive position in proteomics and in the development of oncology
products.   Before  we  recover  development   expenses  for  our  products  and
technologies,  the products or  technologies  may become obsolete as a result of
technological  developments  by us or others.  Our  products  could also be made
obsolete by new technologies which are less expensive or more effective.  We may
not be able to make the  enhancements  to our  technology  necessary  to compete
successfully with newly emerging technologies.

We have experienced fluctuating results of operations.

Our results of operations  have  fluctuated on an annual and quarterly basis and
may fluctuate  significantly  from period to period in the future, due to, among
other factors:

- -    variations in revenue from sales of and royalties from our products;

- -    timing of regulatory approvals and other regulatory  announcements relating
     to our products;

- -    variations in our marketing, manufacturing and distribution channels;


                                      -5-
<PAGE>

- -    timing of the  acquisition  and  successful  integration  of  complementary
     products and technologies;

- -    timing  of new  product  announcements  and  introductions  by us  and  our
     competitors; and

- -    product obsolescence resulting from new product introductions.

Many of these factors, and others not listed above, are outside our control. Due
to one or more of these  factors,  our results of operations  may fall below the
expectations  of  securities  analysts  and  investors  in  one or  more  future
quarters. If this happens, the market price of our common stock could decline.

We rely heavily on our collaborative partners.

Our success  depends in significant  part upon the success of our  collaborative
partners.  We  have  entered  into  the  following  agreements  for  the  sales,
marketing,  distribution and manufacture of our products, product candidates and
technologies:

- -    sub-license and marketing agreement with Berlex Laboratories, Inc. relating
     to the  Quadramet  technology  which  we  licensed  from  The Dow  Chemical
     Company. Berlex is responsible for marketing, selling and arranging for the
     manufacture  and  distribution  of  Quadramet  in the United  States.  This
     agreement  expires on the later of October 28, 2018 or upon the  expiration
     of the patents covering Quadramet;

- -    agreement  for  manufacture  of  Quadramet  by The  DuPont  Pharmaceuticals
     Company  (formerly  the  radiopharmaceuticals  division of The DuPont Merck
     Company);

- -    marketing and platform development agreement with Informax, Inc. related to
     our proteomics program;

- -    a joint venture with Progenics Pharmaceuticals, Inc. for the development of
     PSMA for immunotherapy for prostate and other cancers; and

- -    letter of intent for a licensing agreement with Molecular Staging, Inc. for
     technology to be used in developing  in vitro  diagnostic  tests using PSMA
     and PSA.

Because our  collaborative  partners are  responsible  for certain of our sales,
marketing,  manufacturing  and  distribution  activities,  these  activities are
outside our direct control.  We cannot assure you that our partners will perform
their  obligations  under  these  agreements  with  us.  In the  event  that our
collaborative  partners  do not  successfully  market and sell our  products  or
breach  their  obligations  under  our  agreements,  our  products  may  not  be
commercially successful,  any success may be delayed and new product development
could be inhibited.

Our  business  could be harmed if our  collaborations  expire or are  terminated
early.

We cannot assure you that we will be able to maintain our existing collaborative
arrangements.  If they expire or are terminated,  we cannot assure you that they
will be renewed or that new arrangements  will be available on acceptable terms,
if at all.  In  addition,  we cannot  assure  you that any new  arrangements  or
renewals of existing  arrangements  will be successful,  that the parties to any
new or  renewed  agreements  will  perform  adequately  or  that  any  potential
collaborators will not compete with us.

We cannot assure you that our existing or future collaborations will lead to the
development of product  candidates or technologies  with  commercial  potential,
that we will be able to obtain  proprietary  rights or licenses for  proprietary
rights for our product  candidates or technologies  developed in connection with
these  arrangements  or that we will be able to ensure  the  confidentiality  of
proprietary rights and information developed in such arrangements or prevent the
public disclosure thereof.

We have limited sales, marketing and distribution capabilities for our products.

                                      -6-
<PAGE>

We recently established a sales force and have limited internal sales, marketing
and  distribution  capabilities  for our  products.  We depend on Berlex for the
sale, marketing and distribution of Quadramet in the United States. In locations
outside the United States, we have not established a selling presence. If we are
unable to establish and maintain  significant sales,  marketing and distribution
efforts,  either  internally or through  arrangements  with third  parties,  our
business may be harmed.

There are risks associated with the manufacture of our products.

If we are to be  successful,  our products will have to be  manufactured  either
internally or through  third-party  manufacturers  in compliance with regulatory
requirements and at costs acceptable to us. We cannot assure you that we will be
able to continue to manufacture,  arrange for manufacture on reasonable terms or
successfully  outsource the  manufacturing of our products.  If we are unable to
successfully  manufacture  or arrange for the  manufacture  of our  products and
product  candidates,  we would  not be able to  successfully  commercialize  our
products and our business may be seriously harmed.

Our business may be adversely  affected by the  uncertainty  associated with our
third-party manufacturers' dependence on single source suppliers.

Quadramet is  manufactured  by DuPont  pursuant to an agreement with both Berlex
and Cytogen. Some components of Quadramet, particularly Samarium/153/ and EDTMP,
are  provided  to  DuPont  by  outside  suppliers.  Due  to  radioactive  decay,
Samarium/153/   must  be  produced  on  a  weekly  basis.   DuPont  obtains  its
requirements for Samarium/153/ from one supplier.  Alternative sources for these
components may not be readily available.  On one occasion,  DuPont was unable to
manufacture  Quadramet  on a timely  basis due to the failure of its supplier to
provide  Samarium/153/.  If DuPont  cannot obtain  sufficient  quantities of the
components on commercially  reasonable terms, or in a timely manner, it would be
unable to  manufacture  Quadramet  on a timely and cost-  effective  basis which
could affect our ability to generate sufficient revenues to become profitable.

Compliance with manufacturing regulations is critical to our business.

We and our  third-party  manufacturers  are required to adhere to US Food & Drug
Administration   regulations   setting  forth   requirements  for  current  Good
Manufacturing  Practices,  or cGMP, and similar  regulations in other countries,
which include extensive testing, control and documentation requirements. Ongoing
compliance with cGMP, labeling and other applicable regulatory  requirements are
monitored  through  periodic  inspections  and market  surveillance by state and
federal  agencies,  including  the  FDA,  and by  comparable  agencies  in other
countries.  Failure  of  our  third-party  manufacturers  or us to  comply  with
applicable  regulations could result in sanctions being imposed on us, including
fines,  injunctions,  civil  penalties,  failure  of  the  government  to  grant
premarket  clearance  or  premarket  approval of drugs,  delays,  suspension  or
withdrawal of approvals, seizures or recalls of products, operating restrictions
and criminal prosecutions.

Failure of consumers to obtain adequate  reimbursement  from third-party  payors
could limit market  acceptance and affect  pricing of our products,  which would
materially adversely affect our business.

Our business,  financial condition and results of operations will continue to be
affected by the efforts of governments and other  third-party  payors to contain
or reduce the costs of  healthcare.  There have been,  and we expect  that there
will  continue  to be, a number of  federal  and state  proposals  to  implement
government  control of pricing and  profitability  of therapeutic and diagnostic
imaging  agents such as our products.  In addition,  an emphasis on managed care
increases  possible  pressure  on  pricing  of these  products.  While we cannot
predict whether these  legislative or regulatory  proposals will be adopted,  or
the effects  these  proposals or managed care efforts may have on our  business,
the  announcement  of these  proposals  and the  adoption of these  proposals or
efforts  could affect our stock price or our  business.  Further,  to the extent
these  proposals or efforts have a material  adverse  effect on other  companies
that are our prospective corporate partners,  our ability to establish strategic
alliances may be adversely affected.

Sales of our  products  depend in part on  reimbursement  to the  consumer  from
third-party payors,  including  Medicare,  Medicaid and private health insurance
plans.  Third-party  payors are increasingly  challenging the prices charged for
medical  products and  services.  We cannot assure you that our products will be
considered  cost-effective  and that reimbursement to consumers will continue to
be  available,  or will be  sufficient  to allow us to sell  our  products  on a

                                      -7-
<PAGE>

competitive basis.  Approval of our products for reimbursement by a third- party
payor may depend on a number of factors,  including  the  payor's  determination
that our products are clinically useful and cost-effective,  medically necessary
and not  experimental or  investigational.  Reimbursement  is determined by each
payor individually and in specific cases. The reimbursement  process can be time
consuming.  If we  cannot  secure  adequate  third-party  reimbursement  for our
products,  there would be a material  adverse effect on our business,  financial
condition and results of operations.

Our potential oncology products will be subject to the risks of failure inherent
in  the  development  of  diagnostic  or  therapeutic   products  based  on  new
technologies.

Product  development  involves a high degree of risk.  We cannot assure you that
the product  candidates  we  develop,  pursue or offer will prove to be safe and
effective,  will  receive  the  necessary  regulatory  approvals,  will  not  be
precluded by  proprietary  rights of third  parties or will  ultimately  achieve
market acceptance.  These product candidates will require substantial additional
investment,  laboratory  development,  clinical testing and regulatory approvals
prior  to  their  commercialization.  We  cannot  assure  you  that we will  not
experience  difficulties that could delay or prevent the successful development,
introduction  and  marketing  of new  products.  If we are unable to develop and
commercialize products on a timely basis or at all, our business will be harmed.

Before we obtain  regulatory  approvals  for the  commercial  sale of any of our
products under development,  we must demonstrate through preclinical studies and
clinical  trials that the product is safe and efficacious for use in each target
indication.  The results from preclinical  studies and early clinical trials may
not be predictive of results that will be obtained in  large-scale  testing.  We
cannot  assure you that our  clinical  trials  will  demonstrate  the safety and
efficacy  of any  products or will result in  marketable  products.  A number of
companies in the biotechnology  industry have suffered  significant  setbacks in
advanced  clinical  trials,  even after  promising  results  in earlier  trials.
Clinical trials or marketing of any potential diagnostic or therapeutic products
may expose us to liability claims for the use of these diagnostic or therapeutic
products.  We may not be able to  obtain  product  liability  insurance  or,  if
obtained,  sufficient  coverage may not be available  at a reasonable  cost.  In
addition,  as we develop diagnostic or therapeutic products internally,  we will
have to make  significant  investments  in  diagnostic  or  therapeutic  product
development,  marketing, sales and regulatory compliance resources. We will also
have to  establish  or  contract  for the  manufacture  of  products,  including
supplies of drugs used in clinical trials,  under the current Good Manufacturing
Practices  of the FDA. We also cannot  assure you that  product  issues will not
arise following successful clinical trials and FDA approval.

The rate of  completion  of clinical  trials also depends on the rate of patient
enrollment.  Patient enrollment  depends on many factors,  including the size of
the patient population, the nature of the protocol, the proximity of patients to
clinical  sites and the  eligibility  criteria for the study.  Delays in planned
patient enrollment may result in increased costs and delays,  which could have a
harmful effect on our ability to develop the products in our pipeline.

If we are unable to comply with applicable governmental regulations,  we may not
be able to continue our operations.

Any products tested, manufactured or distributed by us or on our behalf pursuant
to  FDA  clearances  or  approvals  are  subject  to  pervasive  and  continuing
regulation by numerous regulatory  authorities,  including primarily the FDA. We
may be slow to adapt, or we may never adapt to changes in existing  requirements
or  adoption  of new  requirements  or  policies.  Our  failure  to comply  with
regulatory  requirements  could  subject  us to  enforcement  action,  including
product seizures, recalls,  withdrawal of clearances or approvals,  restrictions
on or injunctions  against  marketing our products based on our technology,  and
civil and criminal penalties.  We cannot assure you that we will not be required
to incur  significant costs to comply with laws and regulations in the future or
that  laws or  regulations  will  not  create  an  unsustainable  burden  on our
business.

Numerous federal, state and local governmental authorities, principally the FDA,
and similar  regulatory  agencies in other  countries,  regulate the preclinical
testing,  clinical trials,  manufacture and promotion of any compounds or agents
we or our collaborative partners develop, and the manufacturing and marketing of
any resulting  drugs.  The drug  development and regulatory  approval process is
lengthy, expensive, uncertain and subject to delays.

                                      -8-
<PAGE>

The regulatory risks we face also include the following:

- -    any compound or agent we or our collaborative partners develop must receive
     regulatory  agency  approval  before  it may  be  marketed  as a drug  in a
     particular country;

- -    the regulatory  process,  which includes  preclinical  testing and clinical
     trials of each  compound  or agent in order to  establish  its  safety  and
     efficacy,  varies from country to country, can take many years and requires
     the expenditure of substantial resources;

- -    in  all  circumstances,  approval  of  the  use  of  previously  unapproved
     radioisotopes  in certain of our products  requires  approval of either the
     Nuclear Regulatory  Commission or equivalent state regulatory  agencies.  A
     radioisotope is an unstable form of an element which undergoes  radioactive
     decay,  thereby emitting radiation which may be used, for example, to image
     or  destroy  harmful  growths  or  tissue.  We cannot  assure you that such
     approvals will be obtained on a timely basis, or at all;

- -    data obtained from  preclinical and clinical  activities are susceptible to
     varying  interpretations  which could  delay,  limit or prevent  regulatory
     agency approval; and

- -    delays or rejections  may be  encountered  based upon changes in regulatory
     agency  policy during the period of drug  development  and/or the period of
     review of any  application  for regulatory  agency  approval.  These delays
     could   adversely   affect  the   marketing  of  any  products  we  or  our
     collaborative   partners   develop,   impose  costly  procedures  upon  our
     activities,   diminish  any  competitive  advantages  we  or  collaborative
     partners may attain and adversely affect our ability to receive royalties.

We cannot  assure you that,  even after  this time and  expenditure,  regulatory
agency  approvals will be obtained for any compound or agent  developed by or in
collaboration with us. Moreover,  regulatory agency approval for a drug or agent
may entail  limitations  on the  indicated  uses that could limit the  potential
market for any such drug.  Furthermore,  if and when such  approval is obtained,
the marketing, manufacture,  labeling, storage and record keeping related to our
products would remain subject to extensive regulatory requirements. Discovery of
previously unknown problems with a drug, its manufacture or its manufacturer may
result in  restrictions  on such drug,  manufacture or  manufacturer,  including
withdrawal  of the drug  from the  market.  Failure  to comply  with  regulatory
requirements  could  result  in  fines,   suspension  of  regulatory  approvals,
operating restrictions and criminal prosecution.

The U.S. Food, Drug and Cosmetics Act requires that our products be manufactured
in FDA registered facilities subject to inspection.  The manufacturer must be in
compliance  with  cGMP,  which  imposes  certain  procedural  and  documentation
requirements   upon  us,  and  our   manufacturing   partners  with  respect  to
manufacturing  and  quality  assurance  activities.  If we or our  manufacturing
partners  do not  comply  with cGMP we may be subject  to  sanctions,  including
fines, injunctions,  civil penalties,  recalls or seizures of products, total or
partial  suspension of production,  failure of the government to grant premarket
clearance or premarket approval for drugs, withdrawal of marketing approvals and
criminal prosecution.

We depend on attracting and retaining key personnel.

We are  highly  dependent  on  the  principal  members  of  our  management  and
scientific  staff.  The  loss of their  services  might  significantly  delay or
prevent the  achievement  of development  or strategic  objectives.  Our success
depends  on our  ability  to retain  key  employees  and to  attract  additional
qualified employees.  Competition for personnel is intense, and we cannot assure
you that we will be able to retain  existing  personnel  or  attract  and retain
additional highly qualified employees in the future.

We have an employee  retention  agreement with our President and Chief Executive
Officer,  H. Joseph Reiser,  Ph.D.,  which provides for vesting of stock options
for the purchase of shares of our common stock based on continued employment and
on the achievement of performance  objectives defined by the board of directors.
We do not have similar retention agreements with our other key personnel.  If we
are unable to hire and retain  personnel in key  positions,  our  management and
operations will suffer unless a qualified replacement can be found.

                                      -9-
<PAGE>

Our  business  exposes  us to  potential  liability  claims  that may exceed our
financial  resources,  including  our  insurance  coverage,  and may lead to the
curtailment or termination of our operations.

Our  business is subject to product  liability  risks  inherent in the  testing,
manufacturing  and marketing of our products.  We cannot assure you that product
liability  claims will not be  asserted  against  us, our  collaborators  or our
licensees. While we currently maintain product liability insurance in amounts we
believe are  adequate,  we cannot assure you that such coverage will be adequate
to protect us against future product  liability claims or that product liability
insurance  will be  available  to us in the  future on  commercially  reasonable
terms,  if at all.  Furthermore,  we cannot  assure  you that we will be able to
avoid significant  product liability claims and adverse publicity.  If liability
claims  against  us exceed  our  financial  resources  we may have to curtail or
terminate our operations.

Our business involves environmental risks that may result in liability for us.

We are subject to a variety of local, state and federal  government  regulations
relating to storage, discharge, handling, emission, generation,  manufacture and
disposal of toxic,  infectious or other hazardous substances used to manufacture
our products.  If we fail to comply with these  regulations,  we could be liable
for damages, penalties or other forms of censure.

If our patent applications do not result in issued patents, then our competitors
may obtain rights to commercialize our discoveries.

Our business and competitive positions are dependent upon our ability to protect
our  proprietary  technology.  Because  of the  substantial  length  of time and
expense  associated with  development of new products,  we, like the rest of the
biopharmaceutical  industry,  place  considerable  importance  on obtaining  and
maintaining  patent and trade secret protection for new  technologies,  products
and  processes.  We  have  filed  patent  applications  for our  technology  for
diagnostic  and  therapeutic  products and the methods for their  production and
use.

The patent  positions of  pharmaceutical,  biopharmaceutical  and  biotechnology
companies,  including us, are generally  uncertain and involve complex legal and
factual questions.  Our patent applications may not protect our technologies and
products because of the following reasons:

- -    there is no  guarantee  that any of our pending  patent  applications  will
     result in additional issued patents;

- -    we may develop additional proprietary technologies that are not patentable;

- -    there is no guarantee that any patents issued to us, our  collaborators  or
     our licensors will provide a basis for a commercially viable product;

- -    there is no guarantee  that any patents  issued to us or our  collaborators
     will provide us with any competitive advantage;

- -    there is no guarantee  that any patents  issued to us or our  collaborators
     will not be challenged, circumvented or invalidated by third parties; and

- -    there is no  guarantee  that any  patents  previously  issued  to others or
     issued in the future  will not have an adverse  effect on our ability to do
     business.

In  addition,  patent  law in the  technology  fields  in  which we  operate  is
uncertain  and still  evolving,  and we cannot  assure  you as to the  degree of
protection  that will be  afforded  any  patents we are  issued or license  from
others.  Furthermore,  we cannot  assure you that others will not  independently
develop similar or alternative technologies,  duplicate any of our technologies,
or, if  patents  are  issued to us,  design  around  the  patented  technologies
developed by us. In addition,  we could incur substantial costs in litigation if
we are required to defend  ourselves  in patent suits by third  parties or if we
initiate  such suits.  We cannot  assure you that,  if  challenged  by others in
litigation,  the patents we have been issued,  or which we have been assigned or
have licensed from others will not be found  invalid.  We cannot assure you that
our  activities  would  not  infringe  patents  owned  by  others.  Defense  and
prosecution  of  patent  matters  can  be  expensive  and  time-consuming   and,
regardless  of  whether  the  outcome  is  favorable  to us,  can  result in the

                                      -10-
<PAGE>

diversion of substantial financial,  managerial and other resources.  An adverse
outcome could:

- -    subject us to significant liability to third parties;

- -    require us to cease any related  research and  development  activities  and
     product sales; or

- -    require us to obtain licenses from third parties.

We cannot  assure  you that any  licenses  required  under any such  third-party
patents or proprietary rights would be made available on commercially reasonable
terms, if at all.  Moreover,  the laws of certain  countries may not protect our
proprietary rights to the same extent as U.S. law.

The issuance of patents may not provide us with sufficient protection.

We depend on our patents and proprietary rights. The issuance of a patent is not
conclusive as to its validity or enforceability,  nor does it provide the patent
holder with freedom to operate  without  infringing the patent rights of others.
Our patents and the patents we license could be challenged by litigation and, if
the outcome of such litigation was adverse, competitors could be free to use the
subject matter covered by the patent, or we may license the technology to others
in  settlement  of  such   litigation.   Invalidation  of  our  key  patents  or
non-approval  of pending  patent  applications  could increase  competition.  In
addition,  any  application or  exploitation  of our  technology  could infringe
patents or proprietary rights of others and any licenses that we might need as a
result  of  such  infringement  might  not be  available  to us on  commercially
reasonable terms, if at all.

We cannot predict whether our or our  competitors'  pending patent  applications
will result in the issuance of valid patents.  Litigation, which could result in
substantial  cost to us,  may  also be  necessary  to  enforce  our  patent  and
proprietary  rights  and/or  to  determine  the scope and  validity  of  others'
proprietary  rights. We may participate in interference  proceedings that may in
the future be declared by the Patent and Trademark Office to determine  priority
of invention,  which could result in substantial  cost to us. The outcome of any
litigation or interference proceeding might not be favorable to us, and we might
not be able to obtain  licenses to  technology  that we require at a  reasonable
cost, if at all.

We are a defendant in litigation  filed against us in the United States  Federal
Court for the District of New Jersey by M. David  Goldenberg  and  Immunomedics,
Inc. We were served with this lawsuit on March 17, 2000. The  litigation  claims
that  our  ProstaScint  product  infringes  a  patent  purportedly  held  by the
plaintiffs.  We believe that the  purported  patent sought to be enforced in the
litigation has now expired.  As a result,  the claim, even if successful,  would
not result in a bar of the continued  sale of ProstaScint or affect any other of
our products or  technology.  However,  given the  uncertainty  associated  with
litigation, we cannot give any assurance that the litigation could not result in
a material expenditure to us.

The  termination  of one or more license  agreements  that are  important in the
manufacture  of our current  products and new product  research and  development
activities would harm our business.

We are a  party  to  license  agreements  under  which  we  have  rights  to use
technologies  owned by other companies in the manufacture of our products and in
our  proprietary  research,  development  and  testing  processes.  We  are  the
exclusive  licensee  of  certain  patents  and patent  applications  held by the
University of North Carolina at Chapel Hill covering part of the technology used
in the proteomics program and of certain patents and patent applications held by
the  Memorial  Sloan-Kettering  Institute  covering  PSMA.  We  depend  upon the
enforceability  of our license  with The Dow  Chemical  Company  with respect to
Quadramet. If the licenses were terminated,  we may not be able to find suitable
alternatives  to this  technology on timely or reasonable  terms, if at all. The
loss  of the  right  to use  these  technologies  that we  have  licensed  would
significantly harm our business.

We  cannot  be  certain  that  our  security  measures  protect  our  unpatented
proprietary technology.

We also rely upon  trade  secret  protection  for some of our  confidential  and
proprietary  information that is not subject matter for which patent  protection
is  being  sought.  To help  protect  our  rights,  we  require  all  employees,
consultants, advisors and collaborators to enter into confidentiality agreements
that require  disclosure,  and in most cases,  assignment to us, of their ideas,

                                      -11-
<PAGE>

developments,  discoveries and  inventions,  and that prohibit the disclosure of
confidential  information  to anyone  outside  Cytogen.  We cannot  assure  you,
however,  that these agreements will provide  adequate  protection for our trade
secrets,  know-how  or  other  proprietary  information  in  the  event  of  any
unauthorized use or disclosure.

If we make any  acquisitions,  we will  incur a  variety  of costs and may never
realize the anticipated benefits.

If  appropriate  opportunities  become  available,  we may  attempt  to  acquire
businesses,  technologies,  services or products that we believe are a strategic
fit with our business.  We currently  have no  commitments  or  agreements  with
respect to any acquisitions other than those described in this prospectus. If we
do  undertake  any  transaction  of this sort,  the  process of  integrating  an
acquired  business,  technology,  service  or product  may  result in  operating
difficulties and expenditures and may absorb  significant  management  attention
that would  otherwise  be available  for ongoing  development  of our  business.
Moreover,  we may never  realize the  anticipated  benefits of any  acquisition.
Future  acquisitions  could result in potentially  dilutive  issuances of equity
securities,  the incurrence of debt,  contingent  liabilities  and  amortization
expenses  related to goodwill and other intangible  assets.  These factors could
adversely affect our results of operations and financial condition,  which could
cause a decline in the market price of our common stock.

Our stock price has been and may continue to be volatile, and your investment in
our stock could decline in value.

The market prices for securities of biotechnology and  pharmaceutical  companies
have  historically  been highly  volatile,  and the market has from time to time
experienced  significant price and volume fluctuations that are unrelated to the
operating  performance of particular  companies.  The market price of our common
stock has fluctuated over a wide range and may continue to fluctuate for various
reasons, including, but not limited to, announcements concerning our competitors
or us regarding:

- -    results of clinical trials;

- -    technological innovations or new commercial products;

- -    changes  in  governmental  regulation  or  the  status  of  our  regulatory
     approvals or applications;

- -    changes in earnings;

- -    changes in health care policies and practices;

- -    developments or disputes concerning proprietary rights;

- -    litigation or public  concern as to safety of the our  potential  products;
     and

- -    changes in general market conditions.

We have adopted  various  anti-takeover  provisions  which may affect the market
price of our common stock.

Our Board of Directors has the authority,  without further action by the holders
of common stock, to issue from time to time, up to 5,400,000 shares of preferred
stock in one or more classes or series, and to fix the rights and preferences of
the  preferred  stock.  Pursuant  to these  provisions,  we have  implemented  a
stockholder  rights plan by which one preferred stock purchase right is attached
to each share of common stock, as a means to deter coercive takeover tactics and
to prevent an acquirer  from  gaining  control of us without  some  mechanism to
secure a fair price for all of our stockholders if an acquisition was completed.
These  rights  will be  exercisable  if a person  or group  acquires  beneficial
ownership  of 20% or more of our  common  stock and can be made  exercisable  by
action of our board of directors  if a person or group  commences a tender offer
which would  result in such person or group  beneficially  owning 20% or more of
our common stock.  Each right will entitle the holder to buy one  one-thousandth
of a share of a new series of our junior participating  preferred stock for $20.
If any person or group becomes the beneficial owner of 20% or more of our common
stock (with certain  limited  exceptions),  then each right not owned by the 20%

                                      -12-
<PAGE>

stockholder  will  entitle its holder to  purchase,  at the right's then current
exercise price, common shares having a market value of twice the exercise price.
In addition,  if after any person has become a 20% stockholder,  we are involved
in a merger or other business combination  transaction with another person, each
right will entitle its holder (other than the 20%  stockholder) to purchase,  at
the right's then current exercise price,  common shares of the acquiring company
having a value of twice the right's then current exercise price.

We are subject to provisions of Delaware corporate law which, subject to certain
exceptions,  will prohibit us from engaging in any "business combination" with a
person who,  together with  affiliates and  associates,  owns 15% or more of our
common stock for a period of three years following the date that the person came
to own 15% or more of our  common  stock  unless  the  business  combination  is
approved in a prescribed manner.

These   provisions  of  the   stockholder   rights  plan,  our   certificate  of
incorporation, and of Delaware law may have the effect of delaying, deterring or
preventing a change in control of us, may  discourage  bids for our common stock
at a premium over market price and may adversely  affect the market  price,  and
the voting and other rights of the holders, of our common stock.

A large number of our shares are  eligible  for future sale which may  adversely
impact the market price of our common stock.

A large number of shares of common stock already  outstanding,  or issuable upon
exercise of options and warrants,  are eligible for resale,  which may adversely
affect  the market  price of the  common  stock.  As of March 13,  2000,  we had
72,649,096 shares of common stock outstanding. An additional 4,580,331 shares of
common stock are issuable  upon the exercise of  outstanding  stock  options and
warrants.  Substantially all of such shares subject to outstanding options will,
when issued upon exercise  thereof,  be available  for  immediate  resale in the
public market pursuant to currently effective registration  statements under the
Securities  Act of  1933,  as  amended,  or  pursuant  to Rule  701  promulgated
thereunder.

                                      -13-
<PAGE>

                           FORWARD-LOOKING STATEMENTS

     This prospectus includes forward-looking  statements about our business and
results of  operations  that are subject to risks and  uncertainties  that could
cause  our  actual  results  to vary  materially  from  those  reflected  in the
forward-looking  statements.  Words such as "believes,"  "anticipates," "plans,"
"estimates,"   "future,"   "could,"  "may,"  "should,"   "expect,"   "envision,"
"potentially," variations of these words and similar expressions are intended to
identify forward-looking  statements.  Factors that could cause or contribute to
these  differences  include those discussed  previously  under the caption "Risk
Factors"  and  elsewhere  in this  prospectus.  You should  not  unduly  rely on
forward-looking  statements  contained  or  incorporated  by  reference  in this
prospectus.  These forward-looking  statements speak only as of the date hereof.
We disclaim any intent or obligation to update these forward-looking statements.




                              SELLING STOCKHOLDERS

     The following table provides  information  known to Cytogen as of March 13,
2000,  with respect to shares of common stock held and to be offered  under this
prospectus from time to time by the selling stockholders.

<TABLE>
<CAPTION>

                        Shares Owned before the Offering

                                                             Shares       Shares Owned After
Name of Selling Stockholder        Number     Percent    Being Offered      The Offering(1)
- ---------------------------        ------     -------    -------------    ------------------
<S>                              <C>           <C>         <C>                     <C>
Berlex  Laboratories, Inc. (2)   1,000,000     1.38%       1,000,000               0
Jeffrey Swarz (3)                   43,197        *           43,197               0
Terry Vance (3)                     43,197        *           43,197               0
- -----------
</TABLE>

*    Less than 1%

(1)  Assumes all of the shares are sold by the selling stockholder.
(2)  In October  1998,  we  entered  into an  exclusive  agreement  with  Berlex
     Laboratories, Inc. for marketing, selling and arranging for the manufacture
     and distribution of our Quadramet(R)  agent.  Under that agreement,  we are
     obligated  to  register  these  shares for resale with the  Securities  and
     Exchange Commission.  Berlex Laboratories,  Inc. has agreed not to sell its
     shares  for 90  days  following  the  effective  date  of the  registration
     statement  we filed on March 28, 2000  (Registration  No.  333-33436).  Our
     agreement with Berlex  Laboratories,  Inc.  expires on the later of October
     28, 2018 or upon the expiration of the patents covering Quadramet.
(3)  Mr. Swarz and Mr. Vance provided consulting services to Cytogen during 1999
     and received  warrants as part of the compensation for their services.  The
     shares for resale are shares acquired upon exercise of the warrants.

                                      -14-
<PAGE>

                              PLAN OF DISTRIBUTION

     The  shares  of common  stock may be sold from time to time by the  selling
stockholders in one or more  transactions at fixed prices,  market prices at the
time of  sale,  varying  prices  determined  at the  time of sale or  negotiated
prices.  The selling  stockholders  may offer their shares in one or more of the
following transactions:

          -    on any national securities exchange or quotation service at which
               the  common  stock  may be  listed or quoted at the time of sale,
               including the Nasdaq National Market;
          -    in the  over-the-counter  market;
          -    in private transactions;
          -    through options;
          -    by  pledge  to  secure  debts  and  other  obligations;  or
          -    a combination of any of the above transactions.

     If required, we will distribute a supplement to this prospectus to describe
material changes in the terms of the offering.

     The shares of common stock  described in this  prospectus  may be sold from
time to time directly by the selling  stockholders.  Alternatively,  the selling
stockholders  may from time to time offer  shares of common  stock to or through
underwriters,  broker-dealers  or  agents.  The  selling  stockholders  and  any
underwriters,  broker-dealers  or agents that participate in the distribution of
the shares of common stock may be deemed to be "underwriters" within the meaning
of the Securities Act of 1933. Any profits on the sale of shares of common stock
and any compensation received by any underwriter,  broker-dealer or agent may be
deemed to be underwriting discounts and commissions under the Securities Act.

     Any shares  covered by this  prospectus  which qualify for sale pursuant to
Rule 144 under the  Securities  Act may be sold under Rule 144 rather than under
the terms of this prospectus.  The selling  stockholders  may transfer,  will or
gift such shares by other means not described in this prospectus.

     To comply with the  securities  laws of certain  jurisdictions,  the common
stock must be offered or sold only  through  registered  or licensed  brokers or
dealers.  In  addition,  in certain  jurisdictions,  the common stock may not be
offered or sold unless they have been  registered  or  qualified  for sale or an
exemption is available and complied with.

     We will pay all costs and expenses  associated with the registration of the
shares.  All expenses for the issuance of a supplement to this prospectus,  when
requested   by  selling   stockholder(s),   will  be  paid  by  the   requesting
stockholder(s).  The selling  stockholders will pay all underwriting  discounts,
commissions,  transfer taxes and other expenses  associated with the sale of the
shares by them.


                                USE OF PROCEEDS

     We will not receive any proceeds  from the resale of shares of common stock
by the selling stockholders.


                                 LEGAL MATTERS

     The  validity of the issuance of the common  stock  offered  hereby will be
passed upon for us by Donald F. Crane, Jr., Esq.


                                      -15-
<PAGE>

                                    EXPERTS

     Our  financial  statements  contained in our Annual Report on Form 10-K for
the year  ended  December  31,  1999,  and  incorporated  by  reference  in this
registration  statement,  have been audited by Arthur Andersen LLP,  independent
public accountants,  as indicated in their report with respect thereto,  and are
incorporated  herein by reference in reliance upon the authority of said firm as
experts  in giving  said  reports.


                      WHERE YOU CAN FIND MORE INFORMATION

     We are subject to the informational requirements of the Securities Exchange
Act of 1934,  as amended.  Accordingly,  we file annual,  quarterly  and special
reports, proxy statements and other information with the Securities and Exchange
Commission.  You may read and copy any document  that we have filed at the SEC's
public  reference  rooms in  Washington,  D.C., New York, New York, and Chicago,
Illinois.  Please call the SEC at 1-800- SEC-0330 for further information on the
public  reference  rooms. You can obtain copies of our SEC filings at prescribed
rates  from  the  SEC  Public  Reference  Section  at 450  Fifth  Street,  N.W.,
Washington, D.C. 20549. Our SEC filings are also available to you free of charge
at the SEC's web site at http:  //www.sec.gov.

     Shares of our  common  stock  are  traded on the  Nasdaq  National  Market.
Documents  we  have  filed  can be  inspected  at the  offices  of the  National
Association of Securities Dealers,  Inc., Reports Section,  1735 K Street, N.W.,
Washington, D.C. 20006.

     This prospectus is a part of a registration  statement on Form S-3 filed by
us with the SEC under the  Securities Act of 1993, as amended.  This  prospectus
does not contain all of the information set forth in the registration  statement
as parts are omitted in accordance  with the rules and  regulations  of the SEC.
For  further  information  about us and the shares of our common  stock  offered
hereby,  please refer to the  registration  statement and any  amendments to the
registration  statement.  The  registration  statement  may be  inspected at the
public  reference  facilities  maintained  by the SEC at the addresses set forth
above.  Statements in this prospectus about any document filed as an exhibit are
not necessarily complete and, in each instance,  you should refer to the copy of
such  document  filed with the SEC.  Each such  statement  is  qualified  in its
entirety by such reference.

                     INFORMATION INCORPORATED BY REFERENCE

     The SEC allows us to  incorporate by reference the  information  filed with
it, which means that we can disclose  important  information to you by referring
you to those documents.  The information incorporated by reference is considered
to be part of this prospectus, and information that we have filed later with the
SEC will  automatically  update  and  supersede  previously  filed  information,
including information contained in this prospectus.

     We  incorporate  by  reference  the  documents  listed below and any future
filings we will make with the SEC under Sections  13(a),  13(c),  14 or 15(d) of
the Exchange Act until this  offering has been  completed:

          (1)  Annual Report on Form 10-K for the fiscal year ended December 31,
               1999 (File No. 000- 14879); and

          (2)  The description of our common stock contained in the registration
               statement on Form 8-A, (Registration No. 000-14879),  as amended.

     You  may  request  a free  copy  of  these  documents  by  writing  Cytogen
Corporation Corporate Communications,  600 College Road East CN 5308, Princeton,
New Jersey 08540-5308, or by calling us at (609) 750-8224.

                                      -16-
<PAGE>


You should rely only on the information            PROSPECTUS             , 2000
incorporated by reference or provided in
this prospectus or a prospectus supplement
or amendment.  We have not authorized
anyone to provide you with different
information.  We are not making an offer
of these  securities  in any state  where                  1,086,394 Shares
the offer is not  permitted.  Also,  this
prospectus  does not  offer to sell any
securities  other  than the  securities                        CYTOGEN
covered by this  prospectus.  You should
not assume that the information in this
prospectus  or a prospectus  supplement
or amendment is accurate as of any date
other than the date on the front of the                      Common Stock
document.




TABLE OF CONTENTS
- -----------------

Cytogen Corporation .......................................................
Risk Factors ..............................................................
Forward-Looking Statements ................................................
Selling Stockholders ......................................................
Plan of Distribution ......................................................
Use of Proceeds ...........................................................
Legal Matters .............................................................
Experts ...................................................................
Where You Can Find More Information .......................................
Information Incorporated by Reference .....................................



<PAGE>



                                    PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

     We will bear the expenses in connection with the issuance and  distribution
of the securities  being  registered as set forth in the following table. All of
the amounts shown are estimates  except the SEC  registration fee and the Nasdaq
National  Market  listing fee.

     SEC  registration  fee.................................. $ 2,577
     Nasdaq National Market listing fee......................  10,864
     Legal fees and expenses.................................  10,000
     Accounting fees and expenses............................   3,000
     Printing expenses.......................................     200
     Miscellaneous expenses..................................     359
          Total.............................................. $27,000

Item 15.  Indemnification of Directors and Officers.

     Section 145(a) of the General Corporation Law of the State of Delaware (the
"DGCL") provides that a Delaware corporation may indemnify any person who was or
is a party or is  threatened  to be made a party to any  threatened,  pending or
completed action, suit or proceeding, whether civil, criminal, administrative or
investigative  (other than an action by or in the right of the  corporation)  by
reason of the fact that he is or was a director,  officer,  employee or agent of
the  corporation  or is or was  serving at the request of the  corporation  as a
director,  officer,  employee  or agent of another  corporation  or  enterprise,
against expenses,  judgments,  fines and amounts paid in settlement actually and
reasonably incurred by him in connection with such action, suit or proceeding if
he acted in good faith and in a manner he  reasonably  believed  to be in or not
opposed to the best  interests  of the  corporation,  and,  with  respect to any
criminal action or proceeding, had no cause to believe his conduct was unlawful.
Section  145(b) of the DGCL provides that a Delaware  corporation  may indemnify
any  person  who was or is a party  or is  threatened  to be made a party to any
threatened,  pending  or  completed  action  or suit by or in the  right  of the
corporation  to procure a judgment  in its favor by reason of the fact that such
person acted in any of the capacities set forth above, against expenses actually
and reasonably  incurred by him in connection  with the defense or settlement of
such  action  or  suit if he  acted  under  similar  standards,  except  that no
indemnification may be made in respect of any claim, issue or matter as to which
such person shall have been adjudged to be liable to the corporation  unless and
only to the extent that the court in which such action or suit was brought shall
determine that despite the adjudication of liability,  such person is fairly and
reasonably  entitled to be  indemnified  for such expenses which the court shall
deem proper.

     Section 145 of the DGCL further  provides  that to the extent a director or
officer of a corporation has been successful in the defense of any action,  suit
or proceeding  referred to in  subsections  (a) and (b) or in the defense of any
claim,  issue, or matter therein,  he shall be indemnified  against any expenses
actually  and  reasonably  incurred  by  him  in  connection  therewith;   there
indemnification provided for by Section 145 shall not be deemed exclusive of any
rights to which the indemnified party may be entitled;  and that the corporation
may purchase  and  maintain  insurance on behalf of a director or officer of the
corporation against any liability asserted against him or incurred by him in any
such  capacity  or  arising  out  of his  status  as  such  whether  or not  the
corporation would have the power to indemnify him against such liabilities under
Section 145.

     Section  102(b)(7) of the DGCL provides that a corporation  in its original
certificate  of  incorporation  or an  amendment  thereto  validly  approved  by
stockholders  may eliminate or limit personal  liability of members of its board
of  directors  or  governing  body for breach of a  director's  fiduciary  duty.
However,  no such  provision  may eliminate or limit the liability of a director
for  breaching  his duty of loyalty,  failing to act in good faith,  engaging in
intentional  misconduct  or  knowingly  violating  a law,  paying a dividend  or
approving  a stock  repurchase  which was  illegal,  or  obtaining  an  improper
personal benefit.  A provision of this type has no effect on the availability of
equitable  remedies,  such as injunction or rescission,  for breach of fiduciary
duty.  The  Company's  Restated  Certificate  of  Incorporation  contains such a
provision.


                                      II-1
<PAGE>


     The Company's  Certificate of  Incorporation  and By-Laws  provide that the
Company shall indemnify  officers and directors and, to the extent  permitted by
the Board of Directors,  employees and agent of the Company,  to the full extent
permitted  by and in the  manner  permissible  under  the  laws of the  State of
Delaware.  In addition,  the By-Laws  permit the Board of Directors to authorize
the Company to purchase and maintain  insurance  against any director,  officer,
employee or agent of the Company arising out of his capacity as such.

Item 16.  Exhibits.

     Exhibit No.         Description
     -----------         -----------
         5.1             Opinion of Donald F. Crane, Jr., Esq.
        23.1             Consent of Arthur Andersen LLP.
        23.2             Consent of Donald F. Crane, Jr., Esq.
                          (included in Exhibit 5.1)
        24.1             Powers of Attorney.


Item 17.  Undertakings.

          A.   The undersigned registrant hereby undertakes:

               (1)  To file,  during  any  period  in which  offers or sales are
                    being made, a post-effective  amendment to this registration
                    statement:

                    (i)  to include any prospectus  required by section 10(a)(3)
                         of the Securities Act of 1933;

                    (ii) to  reflect  in the  prospectus  any  facts  or  events
                         arising  after the effective  date of the  registration
                         statement (or the most recent post-effective  amendment
                         thereof)  which,  individually  or  in  the  aggregate,
                         represent a fundamental  change in the  information set
                         forth in the  registration  statement.  Notwithstanding
                         the  foregoing,  any  increase or decrease in volume of
                         securities  offered  (if  the  total  dollar  value  of
                         securities  offered  would not  exceed  that  which was
                         registered)  and any deviation from the low or high end
                         of  the  estimated   maximum   offering  range  may  be
                         reflected in the form of prospectus  filed with the SEC
                         pursuant  to Rule  424(b)  if,  in the  aggregate,  the
                         changes  in volume and price  represent  no more than a
                         20% change in the maximum aggregate  offering price set
                         forth in the "Calculation of Registration Fee" table in
                         the effective registration statement;

                    (iii)to include any material information with respect to the
                         plan of  distribution  not previously  disclosed in the
                         registration  statement or any material  change to such
                         information in the registration statement;

               provided,  however, that paragraphs A(l) (i) and A(l) (ii) do not
               apply if the  registration  statement is on Form S-3, Form S-8 or
               Form  F-3,  and the  information  required  to be  included  in a
               post-effective  amendment  by those  paragraphs  is  contained in
               periodic  reports  filed  with  or  furnished  to the  SEC by the
               registrant  pursuant  to  section  13 or  section  15(d)  of  the
               Securities   Exchange  Act  of  1934  that  are  incorporated  by
               reference in the registration statement.

               (2)  That, for the purpose of determining any liability under the
                    Securities Act of 1933, each such  post-effective  amendment
                    shall be deemed to be a new registration  statement relating
                    to the securities offered therein,  and the offering of such
                    securities  at that time  shall be deemed to be the  initial
                    bona fide offering thereof.

               (3)  To remove  from  registration  by means of a  post-effective
                    amendment  any  of the  securities  being  registered  which
                    remain unsold at the termination of this offering.

                                      II-2
<PAGE>

     B.   Undertaking  Regarding Filings  Incorporating  Subsequent Exchange Act
          Documents by Reference.

     The  undersigned   registrant  hereby  undertakes  that,  for  purposes  of
determining  any liability  under the Securities Act of 1933, each filing of the
registrant's  annual  report  pursuant to section  13(a) or section 15(d) of the
Securities  Exchange  Act of 1934  (and,  where  applicable,  each  filing of an
employee  benefit  plan's  annual  report  pursuant  to  section  15(d)  of  the
Securities  Exchange Act) that is incorporated by reference in the  registration
statement  shall be deemed to be a new  registration  statement  relating to the
securities  offered  therein,  and the offering of such  securities at that time
shall be deemed to be the initial bona fide offering thereof.

     C.   Undertaking in Respect of Indemnification.

     Insofar as indemnification for liabilities arising under the Securities Act
of 1933 may be permitted to directors,  officers and controlling  persons of the
registrant pursuant to the foregoing  provisions,  or otherwise,  the registrant
has been advised that in the opinion of the SEC such  indemnification is against
public policy as expressed in the Act and is, therefore,  unenforceable.  In the
event that a claim for indemnification  against such liabilities (other than the
payment by the registrant of expenses incurred or paid by a director, officer or
controlling  person of the registrant in the  successful  defense of any action,
suit or proceeding) is asserted by such director,  officer or controlling person
in connection with the securities being registered,  the registrant will, unless
in the  opinion  of its  counsel  the matter  has been  settled  by  controlling
precedent,  submit to a court of appropriate  jurisdiction  the question whether
such  indemnification by it is against public policy as expressed in the Act and
will be governed by the final adjudication of such issue.


                                      II-3
<PAGE>

                                   SIGNATURES

     Pursuant to the  requirements of the Securities Act of 1933, the registrant
certifies  that it has  reasonable  grounds to believe  that it meets all of the
requirements  for  filing  on Form S-3 and has  duly  caused  this  registration
statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized,  in the City of  Princeton,  New Jersey,  on this 10th day of April,
2000.

                                        CYTOGEN  CORPORATION



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



     Pursuant  to  the   requirements  of  the  Securities  Act  of  1933,  this
registration  statement  has been signed below by the  following  persons in the
capacities and on the dates indicated.
<TABLE>
<CAPTION>


Signature                                       Title                                Date
- ---------                                       -----                                ----
<S>                           <C>                                               <C>
/s/ H. Joseph Rieser
- ----------------------        Chief Executive Officer and President(Principal   April 10, 2000
H. Joseph Reiser                 Executive Officer and Director)


/s/ Jane M. Maida
- ----------------------        VP Finance and Administration (Principal          April 10, 2000
Jane M. Maida                    Accounting Officer)


*
- ----------------------        Director                                          April 10, 2000
John E. Bagalay


*
- ----------------------        Director                                          April 10, 2000
Ronald J. Brenner


*
- ----------------------        Director                                          April 10, 2000
Stephen K. Carter


*
- ----------------------        Director and Chairman of the Board                April 10, 2000
James A. Grigsby


*
- ----------------------        Director                                          April 10, 2000
S. Leslie Misrock


*
- ----------------------        Director                                          April 10, 2000
Robert F. Hendrickson
</TABLE>

  By: /s/ H. Joseph Reiser
      ---------------------
      H. Joseph Reiser
      (Attorney-in-Fact)


                                      II-4

<PAGE>

                                 Exhibit Index
                                 -------------

Exhibit No.         Description
- -----------         -----------
 5.1                Opinion of Donald F. Crane, Jr., Esq.
23.1                Consent of Arthur Andersen LLP.
23.2                Consent of Donald F. Crane, Jr., Esq.
                     (included in Exhibit 5.1).
24.1                Powers of Attorney




April 10, 2000

Cytogen Corporation
600 College Road East  CN 5308
Princeton, NJ  08540-5308

Ladies and Gentlemen:

The  undersigned  has  acted as  counsel  to  Cytogen  Corporation,  a  Delaware
corporation  (the  "Company"),  in connection with the preparation and filing by
the  Company  of  a  registration  statement  on  Form  S-3  (the  "Registration
Statement") including a related prospectus filed with the Registration Statement
(the  "Prospectus"),  covering the registration of up to 1,086,394 shares of the
Common Stock, $.01 par value, of the Company (the "Shares") on behalf of certain
selling stockholders.

In connection with this opinion, I have examined the Registration  Statement and
related  Prospectus,  the Company's  Restated  Certificate of Incorporation  and
Bylaws, as amended, and such other records, documents,  certificates,  memoranda
and other instruments as I have deemed necessary as a basis for this opinion.  I
have assumed the  genuineness  and  authenticity  of all  documents  reviewed as
originals,  the  conformity  to  originals of all  documents  reviewed as copies
thereof and the due execution and delivery of all documents  where due execution
and delivery are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, I am of the opinion that
the Shares are validly issued, fully paid and nonassessable.

I consent to the reference to my name under the caption  "Legal  Matters" in the
Prospectus  included  in the  Registration  Statement  and to the filing of this
opinion as an exhibit to the Registration  Statement.  In giving such consent, I
do not admit  that I come  within  the  category  of  persons  whose  consent is
required under Section 7 of the Securities Act of 1933, as amended.

Very truly yours,


/s/ Donald F. Crane, Jr.
- ------------------------
Donald F. Crane, Jr.



                                                                    Exhibit 23.1


                   CONSENT OF INDEPENDENT PUBLIC ACCOUNTANTS

As independent  public  accountants,  we hereby consent to the  incorporation by
reference in this S-3  registration  statement  of our report dated  January 27,
2000 included in the Company's  Form 10-K for the year ended  December 31, 1999
and to all references to our Firm included in this registration statement.

                                   ARTHUR ANDERSEN LLP
Philadelphia, PA
   April 10, 2000



                                                                    EXHIBIT 24.1


                               POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS,  that each person whose signature  appears below
constitutes  and appoints H. Joseph Reiser,  Jane M. Maida,  or Donald F. Crane,
Jr.,  and each of them,  as his or hers true and  lawful  attorneys-in-fact  and
agents, with full power of substitution and  resubstitution,  for him and in his
name,  place  and  stead,  in any and  all  capacities,  to sign a  registration
statement  on Form  S-3  with  respect  to  registration  for  resale  with  the
Securities and Exchange  Commission of 1,086,394 shares of the common stock $.01
par  value  of the  Company,  and to  sign  any and  all  amendments  (including
post-effective amendments) and supplements to such registration statement or any
prospectus  or  prospectuses  included  therein,  and to file the same  with the
Commission,  granting unto said  attorneys-in-fact and agents, and each of them,
full  power  and  authority  to do and  perform  each and  every  act and  thing
requisite  and  necessary to be done in  connection  therewith,  as fully to all
intents and  purposes as he might or could do in person,  hereby  ratifying  and
confirming all that said  attorneys-in-fact and agents, or any of them, or their
or his substitute or substitutes,  may lawfully do or cause to be done by virtue
hereof.

<TABLE>
Name                     Signature                               Title
- ----                     ---------                               -----

<S>                      <C>                           <C>
H. Joseph Reiser         /s/ H. Joseph Reiser          Chief Executive Officer and
                         -----------------------       President (Principal Executive
                                                       Officer and Director

Jane M. Maida            /s/ Jane M. Maida             Vice President-Finance and
                         ------------------------      Administration
                                                       (Principal Accounting Officer)

John E. Bagalay, Jr      /s/ John E. Bagalay, Jr.      Director
                         -------------------------

Ronald J. Brenner        /s/ Ronald J. Brenner         Director
                         -------------------------

Stephen K. Carter        /s/ Stephen K. Carter         Director
                         -------------------------

James A. Grigsby         /s/ James A. Grigsby          Director
                         -------------------------

Robert F. Hendrickson    /s/ Robert F. Hendrickson     Director
                         -------------------------

S. Leslie Misrock        /s/ S. Leslie Misrock         Director
                         -------------------------
</TABLE>


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