IMCLONE SYSTEMS INC/DE
S-3/A, 1999-01-11
BIOLOGICAL PRODUCTS, (NO DIAGNOSTIC SUBSTANCES)
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     As filed with the Securities and Exchange Commission on January 9, 1999

                                                      Registration No. 333-67335
    

================================================================================
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                           ---------------------------

   
                          PRE-EFFECTIVE AMENDMENT NO. 1
                                       TO
                                    FORM S-3
    

             REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                          IMCLONE SYSTEMS INCORPORATED
             (Exact name of registrant as specified in its charter)

                  Delaware                                 04-2834797
         (State or other jurisdiction of                (I.R.S. Employer
         incorporation or organization)                 Identification No.)

               John B. Landes, Esq.
      Vice President, Business Development
               and General Counsel
           ImClone Systems Incorporated

                180 Varick Street                  180 Varick Street
             New York, New York 10014          New York, New York 10014

                  (212) 645-1405                     (212) 645-1405
      (Name, address, including zip code,     Address, including zip code, and
        and telephone number, area code,  (telephone number, including including
            of agent for service)               area code, of registrant's
                                                principal executive offices)

                          Copies of communications to:

                          Lawrence A. Darby III, Esq.
                  Kaye, Scholer, Fierman, Hays & Handler, LLP
                                425 Park Avenue
                         New York, New York 10022-3598

                           ---------------------------

  Approximate date of commencement of proposed sale to the public: As soon as
        practicable after this Registration Statement becomes effective.

      If the only securities being registered on this Form are being 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, 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. [ ]

   
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 of 1933 or until the Registration Statement shall become
effective on such date as the Commission, acting pursuant to Section 8(a), may
determine.
    

================================================================================

<PAGE>

The information in this prospectus is not complete and may be changed. We may
not sell these securities until the related registration statement filed with
the Securities and Exchange Commission is effective. This prospectus is 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.

   
                   Subject to completion dated January 9, 1999
    

PROSPECTUS

                                 IMCLONE SYSTEMS
                                  INCORPORATED

                                1,731,497 SHARES

                                  COMMON STOCK

THE COMPANY

ImClone Systems Incorporated
180 Varick Street
New York, New York 10014

(212) 645-1405

THE SELLING STOCKHOLDERS

   
Certain of our officers and directors and a member of our Scientific Advisory
Board who participated in the founding of ImClone are having registered hereby
the offer and sale of the Shares which they may acquire by exercising warrants
we have issued to them at various times before the date of this prospectus.
    

TRADING SYMBOL:
NASDAQ NATIONAL MARKET - "IMCL'

THE OFFERING

The Selling Stockholders may sell Shares at various times and in various types
of transactions, including sales in the open market, sales in negotiated
transactions and sales by a combination of these methods. The Selling
Stockholders may sell Shares at the market price of our common stock at the time
of a sale, at prices relating to the market price of our common stock over a
period of time, or at prices negotiated with the buyers of Shares.

The Selling Stockholders will receive all proceeds from the sale of Shares, and
will pay all brokerage fees and commissions and similar sale-related expenses.
We will not receive any of the proceeds. When the Selling Stockholders exercise
their warrants to buy the Shares being sold, they will pay us the exercise
price. We are paying the expenses in connection with the registration of the
shares with the SEC.

This Investment Involves a High Degree of Risk. See "Risk Factors" 
Beginning On Page 9.

      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 January [ ], 1999.
    

<PAGE>

                                TABLE OF CONTENTS

THE COMPANY....................................................................1
THE OFFERING...................................................................1
PROSPECTUS SUMMARY.............................................................1
THE OFFERING...................................................................7
WHERE YOU CAN FIND MORE INFORMATION............................................8
SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS.....................................8
RISK FACTORS...................................................................9
         Early Stage of Product Development; Technological Uncertainty.........9
         History of Operating Losses and Accumulated Deficit...................9
         Cash Requirements; Need for Additional Funding........................9
         Dilution; Shares Available for Future Sale...........................10
         Limited Manufacturing Experience.....................................12
         Establishing Sales and Marketing Capability..........................12
         Dependence on Certain Agreements with Corporate Partners.............12
         Uncertainties as to Patents and Proprietary Technologies.............13
         Reliance on and Attraction and Retention of Key Personnel and 
            Consultants.......................................................14
         Technological Change and Risk of Obsolescence; Competition...........14
         Extensive Government Regulation......................................14
         Product Liability Exposure...........................................15
         Hazardous Materials; Environmental Matters...........................15
         Uncertainty of Health Care Reimbursement and Related Matters.........15
         Possible Volatility of Stock Price...................................15
         Limitations on Net Operating Loss Carryforwards......................15
         Dividend Policy and Restrictions.....................................15
   
         Year 2000............................................................15
    
USE OF PROCEEDS...............................................................16
SELLING STOCKHOLDERS..........................................................17
PLAN OF DISTRIBUTION..........................................................18
         Manner of Sales; Broker-Dealer Compensation..........................18
         Filing of Supplement to Prospectus In Certain Instances..............18
         Certain Persons Deemed to be Underwriters............................18
         Regulation M.........................................................18
LEGAL MATTERS.................................................................18
DISCLOSURE OF COMMISSION POSITION ON INDEMNIFICATION FOR SECURITIES 
  ACT LIABILITIES.............................................................19


                                      -2-
<PAGE>

                          -----------------------------

                               PROSPECTUS SUMMARY

                          -----------------------------

                                   THE COMPANY

      The following summarizes the business and operations of ImClone Systems
Incorporated (referred to in this prospectus as "we", "us", "ImClone" or the
"Company"). This summary highlights certain information about ImClone that is
included and incorporated by reference in this prospectus. This summary is not
complete and does not contain all of the information about us or all of the
information that you should consider before investing in our common stock. You
should read the entire prospectus carefully, including the information under the
caption "Risk Factors" and the information in the financial statements and the
notes to the financial statements that are incorporated by reference in this
prospectus. The securities offered by this prospectus involve a high degree of
risk. See "Risk Factors."

                         Overview of ImClone's Business

      We are a biopharmaceutical company, primarily engaged in the research and
development of drugs and other products for the treatment of cancer and
cancer-related disorders.

      When we have successfully tested our products, we intend to sell them to
the public when and if we receive Food and Drug Administration ("FDA") and any
other required regulatory approvals. We may manufacture and market the products
by ourselves or in cooperation with others.

ImClone's Cancer-Related Products.

      We currently have three cancer-related products that we are developing,
two of which we are testing in clinical trials. A clinical trial is a study in
which a product being tested is administered to patients under the supervision
of a qualified principal investigator. A clinical study is intended to
determine, among other things, the product's safety and effectiveness. We have
not yet commercialized and marketed any of these products or sold them to the
public. We are currently involved in developing the following cancer-related
products:

o  C225 Cancer Therapeutic ("C225").

o  BEC2 Cancer Vaccine ("BEC2").

o  c-p1C11 Chimerized Monoclonal Antibody Inhibitor of Angiogenesis ("c-p1C11").

We discuss each of these products more fully below under the heading "ImClone's
Development Programs."

Licensing of Diagnostics and Infectious Disease
    Products.

      We have also researched, developed and tested products to diagnose, and
vaccines for, infectious diseases such as the sexually transmitted diseases
gonorrhea and chlamydia. We have licensed the rights to these diagnostic and
infectious disease products and vaccines to corporate partners. We use the
licensing, research support and royalty fee revenues that we receive from these
corporate partners, in part, to fund our ongoing research and development of
cancer-related products.

Research Programs.

      In addition to our development programs, we also continue to conduct
research in various areas. We conduct such research to discover new treatments
for cancer. We conduct such research in-house, as well as in cooperation with
certain corporate partners and academic institutions.

Background and Facilities.

      ImClone was incorporated in Delaware in 1984 and began its principal
research and development operations in March 1986. ImClone's principal executive
offices and laboratories are located at 180 Varick Street, New York, New York,
10014, and the telephone number is (212) 645-1405.

      We also operate a facility in Somerville, New Jersey where we manufacture
materials for product candidates of sufficient quality and in sufficient
quantity for human clinical trials.

                         ImClone's Development Programs

C225 Cancer Therapeutic.

      Our main interventional therapeutic product candidate for cancer is a
chimerized (part mouse, part human) monoclonal antibody that blocks the
Epidermal Growth Factor ("EGF") receptor. An interventional therapeutic product
for cancer is a drug that interferes with the growth of tumors, and is used to
treat people who have developed cancer. An antibody is a protein that directly
attacks foreign substances in the body, including tumors. The "monoclonal"
nature of an antibody means that the antibody is derived from a single antibody
producing cell, called a hybridoma cell. C225 works to treat cancer in the same
manner as other growth factor receptor inhibitors, which process is discussed in
greater detail under the heading "ImClone's Research Programs -- Research on
Interventional Therapeutics."

      The EGF receptor is found in excessive amounts in the cells of
approximately one-third of all solid cancers. It is also found in select normal
tissue. In vivo animal studies, which for cancer studies can be studies in which
animals have been implanted with human tumors, have shown that C225, when used
together with various agents used in chemotherapy (doxorubicin, cisplatin or
paclitaxel), helps these chemotherapeutic agents fight the tumors more
effectively. 


                                       1
<PAGE>

These studies showed that the human tumors established in these animals were
eliminated, and the animals survived tumor-free for a significant period of
time. We have also found that C225 used alone helps reduce tumors in animals
that have been implanted with renal cell carcinoma (kidney cancer) and
pancreatic carcinoma (pancreatic cancer).

      Our C225 product is now in clinical trials. Clinical trials are typically
conducted in three sequential phases, Phase I, Phase II and Phase III, although
the phases may overlap. In Phase I, the initial introduction of the drug into
human subjects, the product is tested for safety, dosage tolerance, absorption,
metabolism, distribution and excretion. A Phase II clinical trial studies a
limited number of patients to determine (1) if the drug has any effect on the
disease, (2) the correct dosage of the drug needed to produce the desired effect
and (3) the side effects of the dosage selected.

      Since December 1994, we have initiated several Phase Ib/IIa clinical
trials of C225 at Memorial Hospital (the patient care arm of Memorial
Sloan-Kettering Cancer Center) (referred to as "Sloan-Kettering"), Yale Cancer
Center, University of Virginia, MD Anderson Cancer Center and the University of
Alabama, among others. In these C225 Phase Ib/IIa studies, we have given C225
intravenously at selected doses, both alone and in combination with
chemotherapeutic drugs, to patients with various solid cancers, such as breast,
prostate, head and neck and renal cancers. Certain of these studies are ongoing.
These studies have shown that the drug is generally well-tolerated by patients.

   
      We expect in the near future to begin Phase III clinical trials to further
test C225 in head and neck cancer, in combination with radiation therapy and in
combination with chemotherapy. A "Phase III" clinical trial is conducted
following a Phase II study which has shown that a product is effective and
acceptably safe. "Phase III" trials further evaluate clinical effectiveness and
further test for safety in a greater number of patients at multiple clinical
study sites. We also expect to begin in the near future several additional Phase
II clinical trials to continue to determine the types of tumors on which C225 is
most effective. In these clinical trials, C225 will most likely be used in
combination with chemotherapeutic agents or immune system agents called
cytokines.

      On December 14, 1998, we entered into an agreement with Merck KGaA
("Merck"), a German-based drug company, relating to the development, marketing
and sale of C225. Under this agreement:

o   We have granted Merck exclusive rights to market C225 outside of North
    America. We have retained the right to market C225 within North America.

o   We have retained the rights to be the exclusive manufacturer of C225.

o   We will co-develop C225 in Japan.

      In return, Merck is (1) paying to us $30 million in upfront fees and early
cash-based milestone payments based upon our achievement of certain milestones
set forth in the agreement, (2) paying to us an additional $30 million assuming
we achieve further milestones for which Merck will receive equity in ImClone
which will be priced at varying premiums to the then market price of the common
stock depending upon the timing of the achievement of the respective milestones,
(3) providing to us subject to certain terms a $30 million secured line of
credit or guaranty for the build-out of a manufacturing facility by us for the
commercial production of C225, (4) funding clinical development of C225 outside
of North America, and (5) required to pay us royalties on future sales of C225,
if any. Merck has also agreed not to own greater that 19.9% of our voting
securities through December 3, 2002.

      The Agreement may be terminated (1) by either Merck or ourselves in the
event of the material breach of the other party, (2) by Merck in various other
instances, including (a) at its discretion on any date on which a milestone is
achieved (in which case no milestone payment will be made), or (b) for a
one-year period after first commercial sale of C225, upon Merck's reasonable
determination that the product is economically unfeasible (in which case Merck
is entitled to receive back 50% of the cash based milestones then paid to date,
but only based upon a royalty rate applied to our sales in North America, if
any). In the event of termination of the agreement, the due date for the payment
of the credit for the manufacturing facility will be accelerated, or in the
event of a guaranty, ImClone will be required to use its best reasonable efforts
to release Merck as guarantor. In the event by March 13, 1999 we fail to agree
with Merck on a production concept for the manufacturing facility or Merck fails
to provide us with the credit facility or guaranty then the agreement may be
terminated by either of us, in which case Merck is entitled to receive back all
milestone payments made to date.
    

BEC2 Cancer Vaccine.

      BEC2 is our principal cancer vaccine product candidate. A cancer vaccine
is intended to be given to a patient after initial treatment of a tumor in order
to activate immune responses to protect against local spread, distant metastases
or recurrence of the cancer. It is currently in the clinical development stage.
BEC2 is a monoclonal anti-idiotypic antibody. Anti-idiotypic antibodies are
antibodies directed against the site of another antibody to which antigens bind.
An antigen is a substance in the body that stimulates the body to produce
antibodies and/or T cells to fight disease. T cells are cells that are involved
in the immune system's response to fight disease. In certain cases, the
anti-idiotypic antibody can resemble the original antigen and thus stimulate an
immune system response. Often, such an anti-idiotypic antibody produces a
stronger immune response than the immune response produced by the original
antigen which it resembles. As a result, the immune system of cancer patients
injected with an anti-idiotypic antibody that resembles an antigen on a tumor
will recognize the tumor antigen and destroy the tumor.

      We have tested the BEC2 antibody since 1991 in Phase I clinical trials at
Sloan-Kettering against certain forms of cancer, including both limited disease
and extensive disease small cell lung carcinoma and melanoma (skin cancer).
Limited disease small cell lung carcinoma is limited to the lungs. Extensive
disease small cell lung carcinoma means that the disease has migrated to other
parts of the body. A statistically significant number of patients with small
cell lung carcinoma who participated in a pilot study involving BEC2 at


                                       2
<PAGE>

Sloan-Kettering had a considerably longer disease-free period after treatment
with BEC2 than would otherwise have been expected. We have begun a Phase III
multinational clinical trial for BEC2 in the treatment of limited disease small
cell lung carcinoma, and patient enrollment has begun.

   
      We have entered into an agreement with Merck relating to the manufacture,
marketing and sale of BEC2. Under this agreement:
    

o   We have granted Merck exclusive rights to manufacture and market BEC2
    worldwide but for North America where the parties share the right to
    co-market BEC2.

o   The parties intend that ImClone will be the bulk product manufacturer of
    BEC2 to support worldwide sales.

      In return, Merck (1) is paying us research support, (2) is required to pay
us certain milestone fees, and (3) is required to pay us royalties on future
sales of BEC2 by Merck outside North America, if any.

Chimerized Monoclonal Antibody Inhibitor of
    Angiogenesis.

      We have developed c-p1C11 as an inhibitor of angiogenesis. Angiogenesis is
the natural process of growth of new blood vessels. Vascular Endothelial Growth
Factor ("VEGF") regulates angiogenesis. VEGF is a natural growth factor which is
also produced by tumor cells. Once produced by the tumor, it stimulates the
body's endothelial cells, which are the cells that line all blood vessels, to
grow. This results in the production of new blood vessels and ensures an
adequate blood supply to the tumor. The growth of a tumor depends upon the
growth of new blood vessels in this manner. KDR is a growth factor receptor
found almost exclusively on the surface of human endothelial cells. VEGF must
recognize and bind to this KDR receptor in order to stimulate the endothelial
cells to grow.

      c-p1C11 is a chimerized monoclonal antibody which specifically binds to
the KDR receptor for VEGF. By doing so, it prevents VEGF from binding to that
receptor, which, in turn, blocks endothelial cell growth and inhibits
angiogenesis. The c-p1C11 antibody, therefore, helps inhibit or eliminate cancer
by preventing the growth of new blood vessels and depriving the tumor of the
blood supply that it requires to grow. The c-p1C11 antibody is called
"chimerized" because part of the antibody is derived from a mouse, while the
other part is derived from a human. The benefit of the chimerization of this
antibody in this way is that the human part causes the antibody to be less
immunogenic. That is, it lessens the chance that the body will recognize the
antibody as foreign and reject it. An antibody such as c-p1C11 that inhibits
angiogenesis may also be useful in treating other diseases that, like cancer,
depend on the growth of new blood vessels. Such diseases include diabetic
retinopathy, macular degeneration and rheumatoid arthritis.

      We are now conducting pre-clinical studies before filing an
Investigational New Drug Application with the FDA to allow us to further test
c-p1C11 as a possible cancer therapeutic. Pre-clinical studies are conducted
before the beginning of clinical trials, and include both laboratory evaluation
of the chemistry of the product and animal studies to determine the safety and
effectiveness of the product. The results of the pre-clinical studies are
submitted to the FDA as part of the Investigational New Drug Application.

      We are also working with MRC Collaborative Center in England to prepare a
humanized form of c-p1C11. A "humanized" form of c-p1C11 would essentially be a
human antibody that contains only a minimal amount of mouse components that are
necessary for the antibody to have therapeutic value without resulting in the
body rejecting the antibody. The humanized form of c-p1C11 would serve as a
back-up, in the event that the chimerized c-p1C11 antibody causes an immune
response in the human body due to the presence of the mouse component.

                           ImClone's Research Programs

General.

      In addition to concentrating on our products in development, we perform
ongoing research in a number of related areas. We conduct research in-house. We
also cooperate with corporate partners and academic institutions on research. We
hope that such research efforts will identify, among other things, additional
drugs and techniques to treat and prevent cancer which we can develop, test and
ultimately commercialize to manufacture and sell to the public.

Research on Interventional Therapeutics.

      Tyrosine Kinase Receptor Inhibitors. We are conducting a research program
to develop inhibitors of tyrosine kinase receptors. Tyrosine kinase receptors
are a type of growth factor receptor. Tumor cells often depend on growth factors
to allow the tumor to continue to grow and multiply rapidly. These growth
factors act by binding to tyrosine kinase receptors, which are receptors located
on the surface of cells. When the growth factor binds to the receptor, this
activates the enzyme (kinase) part of the receptor, which initiates an "on
signal" in the cells. The kinase activity initiates the process of cell
division, which results in tumor growth. Therefore, a product that inhibits
tyrosine kinase receptors, would prevent the growth factor from binding with the
tyrosine kinase receptor. This would, in turn, prevent or inhibit the kinase
activity that would result from such binding, as well as the resulting cell
division and tumor cell growth.

      In the past, we have chosen to inhibit tyrosine kinase receptors with
antibodies that block the binding of growth factors to the receptors. More
recently, we have started a discovery program to identify small molecules that
inhibit the enzyme part of growth factor receptors. In October 1997, we entered
into an agreement with CombiChem, Inc., a combinational chemistry company. Under
our agreement, we can use CombiChem's library of structures of chemical
compounds to help us identify candidates that interfere with the function of
growth factor receptors. CombiChem will also synthesize novel and improved
molecules that act as inhibitors of the growth factor receptors. We have also
entered into an agreement with the Institute for Molecular Medicine in Freiburg,
Germany, which permits us to test small molecules as 


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<PAGE>

therapeutic candidates to see if they are effective in inhibiting various
tyrosine kinase receptors.

      VE-cadherin. In connection with our anti-angiogenesis research program, we
are also doing research to see whether antibodies that inhibit vascular-specific
cadherin ("VE-cadherin") also inhibit angiogenesis. Cadherins are a family of
cell surface molecules that help organize tissue structures. Researchers
generally believe that VE-cadherin plays an important role in angiogenesis by
organizing the assembly of endothelial cells into vascular tubes, which is a
necessary step in the formation of new blood vessels. As we stated above,
advanced tumor growth is dependent on the formation of a capillary blood vessel
network in the tumor to ensure an adequate blood supply to the tumor. Therefore,
antibodies that inhibit VE-cadherin may inhibit such capillary formation in
tumors, and help fight cancer by cutting-off an adequate blood supply to the
tumor. We intend to test various monoclonal antibodies against VE-cadherin to
see if they are effective in inhibiting the function of the VE-cadherin, and the
growth of blood vessels.

      We also intend to use our chemical analysis techniques as well as
CombiChem's libraries to identify small molecules, in addition to antibodies,
that inhibit VE-cadherin. In connection with our VE-cadherin research program,
we have been assigned the exclusive rights to VE-cadherin-2, a
recently-developed form of vascular-specific cadherin, and to antibodies that
inhibit VE-cadherin. We also collaborate with the Mario Negri Institute for
Pharmacological Research (Milan, Italy) to do pharmacological research to better
determine the role of VE-cadherin in angiogenesis.


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<PAGE>

   
Research on Potential Cancer Vaccines.
    

      We are conducting research to discover possible cancer vaccines as another
route to cancer treatment. Cancer vaccines would activate immune responses to
tumors to protect against local spread, distant metastases or recurrence of
cancer. We focus our research efforts on choosing appropriate cancer cell
targets and producing effective immune responses in our cancer vaccine research
program.

      For example, we are now doing research on a possible melanoma vaccine
based on the melanoma antigen gp75. A melanoma is a tumor or cancerous growth of
the skin. The gp75 antigen stimulates the body to produce antibodies and T cells
to attack the malignant melanoma. Animal studies have shown that a gp75 cancer
vaccine is very effective in creating an immune response in the body against
melanoma cells, and may prevent or inhibit growth of experimental melanoma
tumors in mice.

   
Research on Endothelial Stem Cell
   Technology.
    

      We have developed the technology necessary to isolate endothelial stem
cells. Endothelial stem cells are cells that may originate in the bone marrow.
These stem cells contribute to the development of new blood vessels throughout
the entire body. Endothelial stem cells help produce endothelial cells. We are
exploring the use of endothelial stem cells to stimulate collateral blood
circulation in ischemias. Ischemias are disease conditions where an organ of the
body does not receive enough blood. For example, a myocardial ischemia is the
clogging of the blood vessels in the heart.

      We believe that the ability to isolate endothelial stem cells could allow
us to use these cells to treat many ischemia conditions by using them to
stimulate the growth of new blood vessels to increase the supply of blood to a
targeted area of the body. We also believe that the isolated endothelial stem
cells could be used to treat other conditions where the stimulation of new blood
vessel growth is desired. These uses include the treatment of burn patients and
the healing of wounds.

      We are also exploring the use of endothelial stem cells in connection with
gene therapy. Gene therapy involves inserting one or more genes into cells. The
cells may then be delivered by various mechanisms to specific parts of the body
in order to treat disease. For example, in diabetes, a condition in which the
pancreas does not produce enough insulin, a gene therapy technique could be used
to alter cells to produce insulin and deliver such insulin producing cells to
the pancreas.

      We believe that a gene therapy delivery approach could also be used with
endothelial cells in order to treat cancer. Tumors require angiogenesis to grow.
Tumors must attract endothelial stem cells in order for angiogenesis to occur.
We believe that a gene therapy technique could be used to alter endothelial stem
cells to express tumor destroying molecules and to deliver these altered
endothelial stem cells to the tumors.

Research on Hematopoiesis.

      We are conducting research in hematopoiesis, which is the growth and
development of blood cell elements. Current cancer treatments such as radiation
and chemotherapy are limited because they are harmful to bone marrow, the part
of the body that manufactures the cellular elements of blood. Radiation and
chemotherapy would be less harmful and could be used more effectively if the
hematopoietic stem cells in the bone marrow (i.e., the cells which make blood
cells) could be shielded from these harmful effects. This could be accomplished
if these blood cell-making stem cells could be removed from the patient before
treatment with radiation or chemotherapy and returned to the patient afterwards.
Therefore, our research, on hematopoiesis has been aimed at discovering factors
to support these blood-making stem cells and to control their proliferation,
differentiation and functional deterioration. Our goal is to permit them to be
maintained in culture outside of the body without harming them.

      Most stem cells, when they are removed from the patient's bone marrow,
quickly differentiate, that is, they become designated for a specific function
and lose their ability to make blood cells. The delta-like protein ("DLK") is a
protein which may help to maintain stem cells in their undifferentiated state
while they are outside the patient's body during radiation treatment or
chemotherapy. We have an exclusive license from The National Institutes of
Health ("NIH") to DLK for use in our studies involving stem cells. DLK may also
be useful in gene therapy using stem cells. DLK could be used to maintain the
stem cells in their undifferentiated state while they are genetically
manipulated outside the body. Then, the stem cells could be returned to the body
as functioning, rather than differentiated, stem cells.

         In the course of our research on hematopoiesis, we discovered the
FLK-2/FLT-3 receptor (originally referred to by ImClone as FLK-2, by others as
FLT-3, and herein as FLK-2/FLT-3). We are the exclusive licensee of a family of
patents and patent applications covering the FLK-2/FLT-3 receptor. FLK-2/FLT-3
ligand is a protein that binds to and activates the FLK-2/FLT-3 receptor. The
FLK-2/FLT-3 ligand's role seems to be to stimulate the growth of the
hematopoietic blood making stem cells. Also, the FLK-2/FLT-3 ligand stimulates
the production of dendritic cells, which are potent cells that specialize in
processing foreign antigens and presenting these antigens to the immune system.
The addition of the FLK-2/FLT-3 ligand to stem cells may help stem cells
reproduce themselves while outside of the body during radiation treatment or
chemotherapy. This would increase the number of stem cells, and speed up the
bone marrow recovery process after return of the stem cells to the patient's
body after treatment.

      We have entered into a non-exclusive license and supply agreement with
Immunex Corporation under which we have granted Immunex a license to the
FLK-2/FLT-3 receptor for the limited use of the manufacture of the FLK-2/FLT-3
ligand. Immunex is currently testing the ligand in human trials for stem cell
stimulation and for tumor inhibition. Under this agreement, we receive royalty
and licensing fees from Immunex, and Immunex has granted us a license to use the
FLK-2/FLT-3 ligand for use in our ex vivo research on stem cells.


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<PAGE>

                 Corporate Partnerships for ImClone's Infectious
                        Disease Vaccines and Diagnostics

      We have licensed our diagnostic and infectious disease vaccine products
and techniques, which are based on our earlier research, to corporate partners
for further development and commercialization.

Diagnostic Technologies.

      We have a strategic alliance with Abbott Laboratories. We have licensed
some of our diagnostic products and techniques to Abbott on a worldwide basis.
In mid-1995, Abbott launched its first DNA-based diagnostic test in Europe,
using our Repair Chain Reaction ("RCR") DNA probe technology. Abbott's test is
used to diagnose the sexually transmitted disease chlamydia. The RCR DNA probe
technology uses DNA amplification techniques to detect the presence of DNA or
RNA in biological samples thereby indicating the presence of disease. Abbott has
since developed tests for other diseases, gonorrhea and mycobacteria, using the
RCR DNA probe technology, and has begun sales of those diagnostic products as
well.

      In December 1996, we amended our agreement with Abbott to allow Abbott to
exclusively license our patented DNA signal amplification technology,
AMPLIPROBE, to Chiron Diagnostics. DNA signal amplification technology such as
AMPLIPROBE also uses DNA amplification techniques to detect the presence of DNA
or RNA in biological samples, thereby indicating the presence of disease. Abbott
receives a royalty payment from Chiron on all sales of Chiron branched DNA
diagnostic probe technology in countries covered by our patents. Abbott, in
turn, pays any such royalties it receives to us. Abbott has recently sold the
Chiron branched DNA diagnostic probe technology to Bayer Pharmaceutical
Corporation.

Infectious Disease Vaccines.

      We have given the Wyeth/Lederle vaccine and pediatrics division of
American Home Products Corporation a worldwide license to manufacture and market
our infectious disease vaccines. These vaccines are being developed by American
Home. In January 1998, we extended our agreement with American Home to allow
them to continue pre-clinical research on these vaccines through September 1999,
in preparation for clinical trials of possible infectious disease vaccines for
the treatment of gonorrhea. Under the modified agreement, American Home must pay
us an annual license fee of $300,000, in semi-annual installments of $150,000
each, until September 1999.

                                    ImClone's
                       Research and Development Operations

In-House Research and Development.

      We began our in-house research and development activities in 1986. Since
that time, we have assembled a scientific staff with complementary skills in a
variety of advanced research technologies, including oncology, immunology,
molecular and cell biology, antibody engineering, protein and synthetic
chemistry and high-throughput screening. We also have a staff of technical and
professional employees who manufacture clinical trial materials at our
Somerville, New Jersey manufacturing facility.

Research and Development with Corporate
    Partners.

      In addition to our in-house research programs, we work with certain
corporations in areas related to our product development efforts. We obtain
funding and other assistance for the development and commercialization of our
products from major pharmaceutical companies in exchange for specific product
licensing rights.

      We intend to enter into additional agreements of this nature with
pharmaceutical companies that have the resources and experience to assist us
financially to help us successfully bring our products to market, both in the
United States and abroad. It is not certain that we will be successful in
entering into any such arrangements.


                                       6
<PAGE>

Research and Development with Academic
   Institutions.

         In addition to our research programs pursued in-house and together with
corporate partners, we work with certain academic institutions to support
research in areas related to our product development efforts. These institutions
include, but are not limited to, the National Cancer Institute, Sloan-Kettering,
the University of California, Princeton University, the University of North
Carolina, The Wistar Institute, The University of Texas Southwestern Medical
Center and The Mario Negri Institute for Pharmacological Research. Usually,
research supported at outside academic institutions is in addition to any
in-house research. We also work with various institutions to perform our
clinical trials. Such institutions include, but are not limited to,
Sloan-Kettering, Yale Cancer Center, the University of Virginia, MD Anderson
Cancer Center, and the University of Alabama.

       THE OFFERING

Common Stock
Being Offered..............   1,731,497 shares.

Selling Stockholders.......   Certain officers and directors of ImClone and a
                              member of our Scientific Advisory Board.

   
Common
Stock
Outstanding
as of December 31,  1998...   24,512,107 shares.

Common Stock
Outstanding After
the Offering...............   25,263,607 shares. This assumes that (1) the
                              Selling Stockholders exercise all their warrants
                              for and sell all Shares covered by this prospectus
                              and (2) we do not issue any new shares of our
                              common stock until the offering is complete.
    

Risk Factors...............   Investing in our common stock is very risky. See
                              "Risk Factors."

Use of Proceeds............   We will not receive any proceeds from the sale of
                              shares in this offering by the Selling
                              Stockholders.

                              If the Selling Stockholders exercise all of their
                              warrants, they will pay us a total of $1,127,250
                              to buy the Shares, not including amounts
                              previously paid to us by Selling Stockholders who
                              have already exercised warrants for Shares. We
                              will use that money for our development programs
                              and for general corporate purposes. See "Use of
                              Proceeds."

NASDAQ National
Market Symbol..............    "IMCL"


                                       7
<PAGE>

                          ----------------------------

                             WHERE YOU CAN FIND MORE
                                   INFORMATION

                          -----------------------------

      We file annual, quarterly and special reports, proxy statements and other
information with the SEC. You may read and copy any document we file 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 these public reference rooms. Our SEC filings are also available to the
public from the SEC's web site at http://www.sec.gov. Our common stock is traded
on the NASDAQ National Market under the ticker symbol "IMCL." You may also read
and copy our SEC filings at the NASDAQ National Market offices located in
Washington, D.C.

      We filed a registration statement on Form S-3 to register the shares
offered by this prospectus with the SEC. As allowed by SEC rules, this
prospectus does not contain all the information that you can find in the
registration statement or the exhibits to the registration statement. The SEC
allows us to "incorporate by reference" the information we file with them. This
means that we can disclose important information to you by referring you to
those documents. The information incorporated by reference is considered to be a
part of this prospectus, except if it is superseded by information in this
prospectus or by later information that we file with the SEC. Information that
we file with the SEC after the date of this prospectus will automatically update
and supersede the information contained or incorporated by reference in this
prospectus. We incorporate by reference the documents listed below, as well as
any future filings we may make with the SEC under Section 13(a), 13(c), 14 or
15(d) of the Securities Exchange Act of 1934, as amended, before the time that
all of the shares offered by this prospectus have been sold or de-registered.
These documents contain important information about our company and its
financial condition.

o     Our Annual Report on Form 10-K for the fiscal year ended December 31,
      1997.

o     Our Quarterly Reports on Form 10-Q for the fiscal quarters ended March 31,
      1998, June 30, 1998 and September 30, 1998.

   
o     Our Current Report on Form 8-K, filed with the SEC on February 10, 1998
      and December 16, 1998.
    

o     The description of our common stock contained in our registration
      statement on Form 8-A filed with the SEC under the Securities Exchange Act
      of 1934, as amended, and any amendment or report filed for the purpose of
      updating that description.

You may request a copy of these filings, excluding all exhibits unless we have
specifically incorporated by reference an exhibit, at no cost, by writing or
telephoning us at:

         ImClone Systems Incorporated
         180 Varick Street
         New York, New York 10014
         (212) 645-1405
         Attention:  Catherine M. Vaczy, Associate
                     General Counsel

      When you are deciding whether to purchase the shares being offered by this
prospectus, you should rely only on the information incorporated by reference or
provided in this prospectus or any supplement. We have not authorized anyone
else to provide you with different information. We are not making any offer of
the shares in any state where the offer is not permitted. You should not assume
that the information in this prospectus or any supplement is accurate as of any
date other than the date on the front of those documents.

                          ----------------------------

                   SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS

                          -----------------------------

      The statements incorporated by reference or contained in this prospectus
discuss our future expectations, contain projections of our results of
operations or financial condition, and include other "forward-looking"
information within the meaning of Section 27A of the Securities Act of 1933, as
amended. Our actual results may differ materially from those expressed in
forward-looking statements made or incorporated by reference in this prospectus.
Forward-looking statements that express our beliefs, plans, objectives,
assumptions or future events or performance may involve estimates, assumptions,
risks and uncertainties. Therefore, our actual results and performance may
differ materially from those expressed in the forward-looking statements.
Forward-looking statements often, although not always, include words or phrases
such as the following:

o    "will likely result"
o    "are expected to"
o    "will continue"
o    "is anticipated"
o    "estimate"
o    "intends"
o    "plans"
o    "projection"
o    "outlook"


                                       8
<PAGE>

      You should not unduly rely on forward-looking statements contained or
incorporated by reference in this prospectus. Factors discussed in the following
documents describe various uncertainties, estimates, assumptions and risks which
may cause actual results or outcomes to differ materially from those expressed
in forward-looking statements. You should read and interpret any forward-looking
statements together with these documents.

o     Our most recent Annual Report on Form 10-K under the captions "Business",
      and "Management's Discussion and Analysis of Financial Condition and
      Results of Operations."

o     Our Quarterly Reports on Form 10-Q.

o     The risk factors contained in this prospectus under the caption "Risk
      Factors."

o     Our other SEC filings.

      Any forward-looking statement speaks only as of the date on which that
statement is made. We will not update any forward-looking statement to reflect
events or circumstances that occur after the date on which such statement is
made.

                          ----------------------------

                                  RISK FACTORS

                          -----------------------------

      An investment in the Shares offered by this prospectus involves a high
degree of risk. You should carefully consider the following factors as well as
the other information contained and incorporated by reference in this prospectus
before deciding to invest in our common stock.

Early Stage of Product Development; Technological
  Uncertainty

         ImClone was founded in 1984, and we opened our laboratory in New York
in 1986. Most of our products are now in research or the early stages of
development or clinical studies. They have not yet been commercialized and
marketed or sold to the public. Therefore, we do not sell or receive any
revenues from sales of these products. At this time, most of our revenues come
from payments we receive from our corporate partners under license and research
arrangements. These revenues have fluctuated significantly in the past, and we
expect them to continue to fluctuate significantly in the future. Therefore, our
results of operations, which are, in part, a function of our revenues, have also
fluctuated in the past, and we expect them to continue to fluctuate
significantly in the future. The level of our revenues and results of operations
at any given time is based primarily on the following factors:

o     The status of development of our various products.

o     The time at which we enter into research and license agreements with
      corporate partners that provide for payments to us, and the timing of
      payments to us under these agreements.

o     Whether or not we achieve specified research or commercialization
      milestones.

o     Timely payment by our corporate partners of amounts payable to us.

o     The addition or termination of research programs or funding support.

o     The timing of sales by Abbott, our partner in diagnostics, of products
      that use our technology, and the amount for which such products are sold.

o     Variations in the level of expenses related to our proprietary products
      during any given period.

      Our products are only in the development stage. Before we can
commercialize our products and begin to sell them to generate revenues, they
will need substantial additional development and clinical testing, which will
cost a lot of money. Generally, to make a profit we will need to successfully
develop, test, introduce and market our products. It is not certain that any of
our products will be successfully developed or that required regulatory
approvals to commercialize them can be obtained. Further, even if we
successfully develop a product, there is no assurance that we will be able to
successfully manufacture or market that product or that customers will buy it.

History of Operating Losses and Accumulated
  Deficit

      We have had significant operating losses and have not earned a profit in
each year since we formed ImClone. These operating losses and failure to be
profitable have been due mainly to the significant amount of money that we have
had to spend on research and development. As of September 30, 1998, we had an
accumulated deficit of approximately $131.0 million. We expect to have
significant additional operating losses over each of the next several years.

Cash Requirements; Need for Additional Funding

Ongoing and Potential Cash Requirements.

      Cash Required for Operations. At this time and for the foreseeable future,
we will need to spend a significant amount of money for, among others, the
following purposes:

o     Ongoing pre-clinical and clinical trials of our existing products.

o     Research and development of new products.

o     Establishing both clinical-scale and commercial-scale manufacturing
      capability in our own facilities and/or in the facilities of others.


                                       9
<PAGE>

o     Marketing our products if we receive necessary regulatory approvals.

      We will need to spend a lot of money to expand our operations. Planned
expansion projects include expanding clinical trials of C225. We will need to
expand and modify our facilities and/or enter into arrangements with others, to
allow us to manufacture enough materials to support these expanded clinical
trials. We also plan to spend money to develop new product candidates and expand
research and development activities. To do this, we will have to hire new
employees, acquire new equipment and enter into new outside research agreements.

      Potential Obligation to Repay Industrial Development Revenue Bonds. In
1990, the New York Industrial Development Agency issued $2.2 million of
Industrial Development Revenue Bonds on which we are responsible for the debt
service. We used the proceeds from that issuance to modify our New York facility
to our specifications. These bonds have a scheduled maturity in 2004, however,
they become due earlier if and when our lease for our New York facility
terminates before that time. Our lease is scheduled to expire in March 1999. We
currently expect to be able to extend the lease. However, if we cannot extend
the lease, then we will be obligated to pay the holders of the bonds a total of
approximately $2.4 million in principal and accrued interest in March 1999. We
cannot be certain that we will be able to extend the lease.

      Dividend Payment Obligations to Holders of Series A Preferred Stock. Under
the terms of our Series A Convertible Preferred Stock, the holder of those
shares is entitled to receive annual dividends of $6.00 per share. If such
dividends are not paid in any year, we remain obligated to pay any unpaid
dividends in future years. Dividends are payable in cash on any Series A
Preferred Shares outstanding on the earlier of (1) annually on December 31st of
each year beginning on December 31, 1999; or (2) at the time of conversion or
redemption of the Series A Preferred Shares on which the dividend is being paid.
Dividends on the Series A Preferred Shares began to accumulate and accrue on
December 15, 1997 (the date of original issuance). As of September 30, 1998,
approximately $1.9 million of dividends had accrued on the Series A Preferred
Shares.

No Assurance of Continued Sources of Capital.

      We will only receive certain future payments from our corporate partners
if we meet specified research and development milestones. We have not yet
achieved some of those milestones and we cannot be certain that we will ever do
so. We also cannot be certain that we will continue to receive expected payments
from our corporate partners. All of the above factors may require us to seek
additional levels of capital through additional arrangements with corporate
partners, equity or debt financings or from other sources. We cannot be certain
that we will be successful in completing any such arrangements or financings. If
adequate funds are not available, then we may be required to significantly cut
back on our planned operations.

Dilution; Shares Available for Future Sale

      General.

   
      The following securities that are convertible into shares of our common
stock were issued and outstanding as of December 31, 1998:

o     Warrants. Various warrants to purchase 2,263,590 shares of our common
      stock, at an average exercise price of approximately $2.79 per share
      (subject to adjustment in certain circumstances).

o     Options. Stock options to purchase 4,339,799 shares of our common stock at
      an average exercise price of approximately $7.82 per share (subject to
      adjustment in certain circumstances).
    

o     Series A Convertible Preferred Stock. 400,000 shares of our Series A
      Convertible Preferred Stock are outstanding. These shares are held by
      Merck. These shares are referred to as the "Series A Preferred Shares." We
      discuss below the general terms on which the Series A Preferred Shares can
      be converted into shares of our common stock.

   
o     Milestone Shares. Under our license agreement with Merck for C225, Merck
      is entitled to receive shares of our common stock (or a non-voting
      preferred stock or other non-voting stock convertible into our common
      stock) in connection with Merck's payment to us of up to $30 million upon
      our achievement of various milestones in the development of C225. These
      shares are referred to as the "Milestone Shares". We discuss below how
      these shares may be obtained.
    

      The market price of our common stock could drop as a result of sales of a
large number of shares of our common stock in the market or the public
perception that such sales could occur. This could make it more difficult for us
to raise money through future offerings of common stock. Therefore, any of the
following events could have a negative effect on our financial condition and
results of operations:

o     The exercise of a significant number of options or warrants.

o     The sale of a substantial number of shares of our common stock acquired
      upon the exercise of options or warrants.

o     The conversion of a significant number of shares of Series A Preferred
      Stock into shares of our common stock.

   
o     The receipt by Merck of a significant number of Milestone Shares.
    

o     The registration by Merck of a significant number of shares of common
      stock received upon the conversion of Series A Preferred Shares and the
      Milestone Shares.


                                       10
<PAGE>

      We do not control the timing of any of these events or the number of
shares issued or sold if any such events take place.

      Warrants and Options.

   
      The shares of our common stock which may be issued under the warrants and
options, including the shares included herein, are either currently registered
with the SEC, or will be registered with the SEC before the shares are purchased
by the holders of the warrants and options.
    

      During the term of the warrants and options, their holders can take
advantage of a rise in the market price of our common stock by purchasing the
shares under the warrants and options at the exercise prices, which may be much
lower than the market price of our common stock. Therefore, the holders of the
options and warrants will most likely exercise them at times when the market
price of our common stock is high with the intention of promptly re-selling the
shares. This will allow them to take the greatest advantage of the relatively
low exercise prices of the options and warrants.

      If we are required to issue shares of our common stock to exercising
holders of warrants and options at below-market prices, our other stockholders
may be negatively affected in two ways:

o     Dilution. The interest of other stockholders will be diluted by the
      issuance of additional shares for below-market purchase prices.

o     Effect on Equity Financings. We will most likely be selling shares of our
      common stock to exercising holders of warrants and options at below-market
      prices (i.e., the exercise prices) at times when we would otherwise prefer
      to be able to sell shares to the public ourselves at the higher market
      prices.

      Series A Preferred Shares.

      100,000 of the Series A Preferred Shares could be immediately converted
into shares of our common stock beginning on December 15, 1997. An additional
100,000 Series A Preferred Shares will be able to be converted into shares of
our common stock on or after each of January 1, 2000, January 1, 2001 and
January 1, 2002.

      Any Series A Preferred Shares converted into common stock before January
1, 2000 will be converted at a conversion price of $12.50 per share of common
stock. After that, the number of shares of common stock into which Series A
Preferred Shares are convertible is not fixed. Instead, the conversion price is
determined under a formula based upon the market price of our common stock at
specified measurement dates, which are generally one year apart. The lower the
market price of our common stock on the measurement date in question, the
greater the number of shares of common stock into which the Series A Preferred
Shares may be converted (i.e., the lower the conversion price). The conversion
price is determined as of the measurement date, and remains fixed until adjusted
on the next measurement date to reflect the market price of our common stock.
During the year 2002, the conversion price is 88% of the market price of our
common stock. This means that the common stock may be purchased at a price that
is 12% lower than the price for which it is being sold on the open market.

      Therefore, it is possible that the conversion price for the Series A
Preferred Shares may be determined as of a measurement date, and the market
price of our common stock may then increase significantly during the period of
time following that measurement date but before the next measurement date. In
such a case, the conversion of a significant number of Series A Preferred Shares
into common stock during that period would dilute our other stockholders. This
is because, in such a situation, we would be required to issue a significant
number of shares of our common stock at a relatively low price (i.e., the
conversion price determined on the most recent measurement date), as compared to
the then market price of our common stock.

      The terms of the Series A Preferred Shares also give us the right, in
certain circumstances, to require the holders of the Series A Preferred Shares
to convert those shares into common stock at the conversion price then in
effect. Generally, if after the determination of the conversion price for the
Series A Preferred Shares on a measurement date, the average market price of our
common stock for any period of five trading days is greater than 150% of that
conversion price, we can require the conversion of the then convertible Series A
Preferred Shares at that conversion price.

   
      Milestone Shares. 

      Under our license agreement with Merck for C225, we are entitled to
receive from Merck up to $60 million upon our achievement of various milestones
in the development of C225. In connection with the final $30 million of these
milestones, Merck is entitled to receive from us Milestone Shares upon making
the applicable milestone payment. The Milestone Shares will be shares of our
common stock (or a non-voting preferred stock or other non-voting stock
convertible into our common stock). The number of shares issued to Merck will be
determined by dividing the particular milestone payment due by the purchase
price of the common stock when the milestone is achieved. The purchase price
will relate to the then market price of our common stock, plus a premium which
varies depending upon whether we achieve the milestone early, on-time or late.
The Milestone Shares will be a non-voting preferred stock or other non-voting
stock convertible into our common stock if the shares of common stock that
otherwise would be issued to Merck would result in Merck owning greater than
19.9% of our common stock. This 19.9% limitation is in place through December
2002. These convertible securities will not have voting rights. They will be
convertible at a price determined in the same manner as the purchase price for
shares of our common stock if shares of common stock were to be issued. They
will not be convertible if as a result of the conversion Merck would own greater
than 19.9% of our common stock. This 19.9% limitation is in place through
December 2002 except that after this date, Merck must sell shares they receive
as a result of conversion to the extent such shares result in their owning in
excess of 19.9% of our common stock.
    


                                       11
<PAGE>

      In addition, we granted Merck certain registration rights regarding the
shares of common stock that they may acquire upon conversion of the Series A
Preferred Shares and Milestone Shares.

Limited Manufacturing Experience.

      We can only be profitable if our products are manufactured in commercial
quantities in compliance with regulatory requirements and at acceptable costs.
So far, we have developed products in the laboratory and, in some cases, we have
produced enough for pre-clinical animal trials and early stage clinical trials.
However, it may be difficult for us to produce large enough quantities for late
stage clinical trials or commercial distribution. If we commercialize any of our
products, we may try to adapt our Somerville, New Jersey manufacturing facility
for such purposes. Alternatively, we may outfit a new facility for use as a
commercial-scale manufacturing facility. However, we have limited experience in
clinical-scale manufacturing and no experience in commercial-scale
manufacturing. Therefore, we cannot be certain that we will be able to
successfully make the transition to late stage clinical or commercial production
of our products.

      We do not know when or if we will need to adapt our existing facility or
outfit a new facility to meet any future clinical-scale or commercial-scale
manufacturing needs. Nor do we know how much such an adaptation or new facility
will cost us. Those variables will depend on many factors beyond our control,
including how quickly our products progress through clinical trials. Therefore,
we may in the future unexpectedly need a significant amount of money to adapt
our facility or build a new facility to accommodate commercial-scale
manufacturing of our products. It is not certain that we will be able to obtain
such funds. If we were not able to do so, we may be required to delay or give up
our plans to commercialize our products and sell them to the public.

   
      Under our license agreement with Merck for C225, Merck has agreed to give
us a secured direct credit facility or a guaranty of up to $30 million for the
build-out of a manufacturing facility for the commercial production of C225. In
the event of termination of the agreement, the due date for our payment of the
credit for the manufacturing facility will be accelerated, or in the event of a
guaranty, we will be required to use our best reasonable efforts to release
Merck as guarantor. In the event by March 13, 1999 we fail to agree with Merck
on a production concept for the manufacturing facility or Merck fails to provide
us with the credit facility or guaranty then the agreement may be terminated by
either of us, in which case Merck is entitled to receive back all milestone
payments made to date.

Establishing Sales and Marketing Capability
    

      Because we are primarily a research and development company, we do not
have a lot of experience in selling or marketing new products. We do not
necessarily plan to market our products on our own. We may decide to do so
initially through, or together with, our corporate partners. See "Risk Factors
- -- Dependence on Certain Contractual Agreements with Corporate Partners." If and
when we want to market a new product on our own, we will need expertise in sales
and marketing. We cannot be certain that we will be able to hire qualified or
experienced sales and marketing personnel or that any marketing or sales efforts
by such personnel will be successful. Under our agreement with Merck for BEC2,
we have the right to co-market BEC2 in North America if it is approved for sale
in North America. Under our agreement with Merck for C225, we have the exclusive
right to market C225 in North America if it is approved for sale in North
America. We also will co-develop C225 with Merck in Japan.

Dependence on Certain Agreements with
  Corporate Partners

      So far, we have earned almost all of our revenues from research and
development funding and license fees and royalties paid to us under agreements
with our corporate partners. We expect this to be the case over the next several
years as well. These agreements usually provide the corporate partner with
certain rights to manufacture and/or market in certain geographic areas
specified products which they develop using our technology. In return, the
corporate partner pays us royalties based on their future sales of those
products, if any. Certain corporate partners give us funding for our research
and development activities. Sometimes, our corporate partners pay us license
fees under these agreements. These license fees may be payable either when we
first enter into an agreement or when and if we or they, depending on the
agreement, reach agreed-upon research, regulatory and commercialization
milestones, or both. We do not receive any of these payments at regular
intervals, and their amounts have fluctuated in the past, and are expected to
continue to fluctuate in the future.

      In most cases, our corporate partners can terminate these arrangements,
including their payment obligations, on relatively short notice under specified
circumstances. In the past, some of these arrangements have in fact been
terminated. We cannot be certain that we will continue to receive revenues from
these arrangements, or that we will enter into any new similar agreements.

      Under these agreements, in most cases, the corporate partner controls and
is responsible for the design and conduct of pre-clinical and clinical trials.
They are also most often also responsible for seeking and obtaining regulatory
approvals and for manufacturing and marketing the products. Therefore, the
amount and timing of funding and the investment of other resources are not
controlled by us. This means that the successful development and sale and
marketing of the products are subject to the risk of financial or other
difficulties that may be experienced by our corporate partners. The amount and
timing of payments we receive under our arrangements with these parties depend
upon all of these variables which are out of our control.

      Also, these corporate partners or their affiliates may be developing their
own products or technologies which may directly compete with products that are
the subject of their arrangement with us. While we believe that our corporate
partners are or will be economically motivated to work toward a successful
arrangement with us, we cannot be certain that their corporate interests and
motivations will remain consistent with ours.


                                       12
<PAGE>

Uncertainties as to Patents and Proprietary
  Technologies

      Generally.

      The patent position of biopharmaceutical companies is generally very
uncertain and involves complex legal and factual questions. Our success will
depend, in part, on whether we can :

o     Obtain patents to protect our own products.

o     Obtain licences to use the technologies of third parties which may be
      protected by patents.

o     Protect our trade secrets and know-how.

o     Operate without infringing the intellectual property and proprietary
      rights of others.

      Patent Rights; Licenses. We may not be able to obtain patents that
adequately protect our own products. Also, our proprietary technologies could
conflict with the rights of others. Our ability to commercialize and market our
products using any such technologies could be materially and negatively
affected.

   
      We have exclusive licenses or assignments of 48 issued patents worldwide.
25 of those are issued U.S. patents. We have exclusive licenses or assignments
of approximately 38 families of patent applications that relate to our
proprietary technology in the U.S. and in foreign countries. We cannot be
certain that patents will be issued as a result of any of these applications.
Nor can we be certain that any issued patents would protect or benefit us or
give us adequate protection from competing products. For example, issued patents
may be challenged and declared invalid. In addition, under many of the
agreements under which we have licenses to the patents or patent applications of
others, we are required to meet specified milestone or diligence requirements in
order to keep our license. We cannot be certain that we will satisfy any of
these requirements.
    

      We hold rights under the patents of certain third parties that we consider
necessary for the development of our technology. We will most likely need to
obtain additional licenses to patents of others in order to commercialize
certain of the products that we are currently developing. We cannot be certain
that we will be able to obtain any such licenses or, if we can do so, how much
they will cost.

      We know that others have filed patent applications in various countries
that relate to several areas in which we are developing products. Some of these
patent applications have already been issued as patents and some are still
pending. The pending patent applications may issue as patents. Issued patents
are entitled to a rebuttable presumption of validity under the laws of the U.S.
and certain other countries. These issued patents may therefore limit our
ability to develop commercial products. If we need licenses to such patents to
permit us to develop or market our products, we cannot be certain that we would
be able to get such licenses on acceptable terms.

      Cost of Intellectual Property Litigation. There has been significant
litigation in the biopharmaceutical industry over patents and other proprietary
rights. Such litigation has cost the parties involved a lot of money. If we
became involved in similar litigation over our intellectual property rights, the
cost of such litigation could be substantial and could have a material negative
effect on us.

      Trade Secrets and Know-How. Certain of our proprietary trade secrets and
unpatented know-how are important to our research and development activities. We
cannot be certain that others will not develop the same or similar technologies
on their own. Although we have taken steps, including entering into
confidentiality agreements with our employees and third parties, to protect our
trade secrets and unpatented know-how and keep them secret, third parties may
still obtain such information.

      Specific Intellectual Property Issues.

      The following are some of the specific areas in which we may be negatively
affected by the patents and patent applications of others:

      C225 Patent Issues. We have an exclusive license to an issued U.S. patent
for the murine form of C225, our EGF receptor antibody product. Our licensor of
this patent, however, did not obtain patent protection outside the U.S. for this
antibody. We have, however, sought additional patent protection for C225 and its
use with chemotherapy and radiation therapy. We have done this by filing
specific patent applications in the U.S. and elsewhere and by exclusively
licensing from a major pharmaceutical company patent applications that relate to
the use of EGF receptor antibodies together with chemotherapy. We are currently
prosecuting these applications. We cannot be certain that we will be successful
in these efforts or that patents will ever be issued.

      C225 is a "chimerized" monoclonal antibody, which means that it is made of
antibody fragments derived from more than one type of animal. Patents have been
issued to other biotechnology companies that cover the chimerization of
antibodies. Therefore, we may be required to obtain licenses under these patents
before we can commercialize our own chimerized monoclonal antibodies, including
C225. We cannot be certain that we will be able to obtain such licenses in the
territories where we want to commercialize, or how much such licenses would
cost.

      BEC2 Patent Issues. We know that others have been issued patents in the
U.S. and Europe covering anti-idiotypic antibodies and/or their use for the
treatment of tumors. These patents, if valid, could be interpreted to cover our
BEC2 monoclonal antibody and certain uses of BEC2. Merck, our worldwide licensee
of BEC2, has informed us that it has obtained non-exclusive, worldwide licenses
to these patents in order to market BEC2 in its territory. We are entitled to
co-promote BEC2 in the U.S., however, we cannot be certain that we could obtain
such licenses on commercially acceptable terms, if at all.

      Angiogenesis Inhibitor Patent Issues. We have patents and have filed
patent applications to protect our proprietary rights to anti-angiogenic
therapeutics, as well as 


                                       13
<PAGE>

therapeutic methods of treating angiogenic disease. We are aware that others
have filed patent applications that could affect our ability to commercialize
some of our anti-angiogenic therapeutics or therapeutic treatments.

      Diagnostic Product Patent Issues. We are aware that third parties have
filed patent applications in areas that could affect our ability or Abbott's
ability to commercialize our diagnostic products. These areas could include
target amplification technology and signal amplification technology. Third party
patents have already been issued in the field of target amplification such as
polymerase chain reaction technology (also known as PCR).

Reliance on and Attraction and Retention of Key
  Personnel and Consultants

      Our ability to successfully develop marketable products and to maintain a
competitive position will depend in large part on our ability to attract and
retain highly qualified scientific and management personnel. We will also need
to develop and maintain relationships with leading research institutions and
consultants. Our success is also very dependent upon the principal members of
our management, scientific staff and Scientific Advisory Board. Competition for
such personnel and relationships is intense, and we cannot be certain that we
will be able to continue to attract and retain such personnel and maintain such
relationships.

Technological Change and Risk of Obsolescence; Competition

      The biopharmaceutical industry is subject to rapid and significant
technological change. We have many competitors, including major drug and
chemical companies, specialized biotechnology firms, universities and other
research institutions. These competitors may develop technologies and products
that are more effective than our products or which would make our technology and
products obsolete and non-competitive. Many of these competitors have much
greater financial and technical resources and production and marketing
capabilities than we do. In addition, many of our competitors have much more
experience than we do in pre-clinical testing and human clinical trials of new
or improved drugs, as well as in obtaining FDA and other regulatory approvals.

      We know of various products being developed or manufactured by competitors
that are used for the prevention, diagnosis or treatment of diseases that we
have targeted for product development. Some of these competitive products use
therapeutic approaches that compete directly with certain of our product
candidates. We have little experience in conducting and managing the
pre-clinical testing necessary to enter the clinical trials that are needed to
obtain government approvals. Therefore, our competitors may succeed in obtaining
FDA approval for their competitive products sooner than we do for ours. This
could hurt our ability to further develop and market our products. Also, if we
do begin significant commercial sales of our products, we will be competing with
the established manufacturing and marketing capabilities of our competitors.
These are areas in which we have limited or no experience. See "Risk
Factors--Limited Manufacturing Experience" and "Risk Factors--Establishing Sales
and Marketing Capability."

Extensive Government Regulation

      The research, pre-clinical development, clinical trials, manufacturing and
marketing of our products are all subject to extensive regulation by U.S. and
foreign governmental authorities. The FDA and similar foreign regulatory
authorities regulate our clinical trials as well as our manufacturing and
marketing operations. They require us to comply with product-specific testing
and approval processes. It may take many years and cost a significant amount of
money to obtain the required regulatory approvals for our products. Once we
begin clinical trials for a new biologic therapeutic or vaccine product, it may
take five to ten years (or more) to receive the required FDA approval to
commercialize that product and begin to sell and market it to the public. We may
need two to six years to develop a new in vitro diagnostic product, depending
upon the clinical data requirements or approval process specified by the FDA for
the approval of the product. The FDA also has the power to request additional
data and to substantially extend these approval processes. Moreover, we cannot
even be certain that we will ultimately receive FDA approval at the end of these
approval processes. In addition, even if granted, product approvals may be
withdrawn or limited at a later time if products do not comply with regulatory
standards or if unexpected problems occur following initial marketing.

      We have not sought or received regulatory approval for the commercial sale
of any of our products or for any manufacturing techniques or facilities. We and
our licensees may experience long delays or excessive costs when we do attempt
to get necessary approvals or licenses. Future federal, state, local or foreign
legislative or administrative acts could also prevent or delay regulatory
approval of our products or the products of our licensees. We cannot be certain
that we or our corporate partners will be able to get the necessary approvals
for clinical testing, manufacturing or marketing of our products, or that the
clinical data we obtain in our studies will be sufficient to establish that our
products are safe and effective. If we fail to get or maintain required
governmental approvals, we or our licensees could be delayed or prevented from
further developing particular products or from marketing our products. Such
failure could also limit the commercial use of the products and therefore have a
material negative effect on their marketability and, in turn, on our liquidity
and financial condition.

Product Liability Exposure

      Because our product candidates are new treatments for diseases, their use
during testing or after approval could expose us to product liability claims. We
cannot be certain that we would have enough money available to satisfy any
liability that might result from any such claims. We try to obtain
indemnification from our corporate partners against certain of these types of
claims. However, we cannot be certain that these parties would choose to honor,
or have the financial resources to honor, any such indemnity obligations. We
carry product liability insurance which covers liabilities that may arise in
connection with pre-clinical and clinical testing of our products. However, we
cannot be certain that this coverage 


                                       14
<PAGE>

will be adequate to protect us in the event of a successful product liability
claim against us.

Hazardous Materials; Environmental Matters

      We use hazardous materials, chemicals, viruses and various radioactive
compounds in our research and development activities. Therefore, we are subject
to federal, state and local laws and regulations governing the use, manufacture,
storage, handling and disposal of these materials and certain waste products. We
believe that our safety procedures for handling and disposing of these materials
comply with the applicable standards. However, we cannot completely eliminate
the risk of accidental contamination or injury from these materials. If such an
accident happened, we could be held liable for any resulting damages. Any such
liability could exceed our financial resources. Also, we may be required to
spend a significant amount of money to comply with environmental laws and
regulations in the future. Current or future environmental laws or regulations
may have a material negative effect on our operations, business or assets.

Uncertainty of Health Care Reimbursement and Related Matters

      Once we have commercialized our products and market them to the public,
our ability to sell them at a reasonable profit may depend, in part, on the
extent to which government health administration authorities, private health
coverage insurers and other organizations reimburse purchasers or users of our
products for the costs of such products and related treatments. If people are
not entitled to adequate healthcare reimbursement for the cost of using our
products, they may not use them or may reduce such use. The reimbursement status
of newly-approved health care products is uncertain, and there can be no
assurance that the reimbursement that will be available to purchasers and users
of our products will be enough to ensure profitable sales of our products.

Possible Volatility of Stock Price

      We believe that the following factors, among others, have caused the
market price of our common stock to fluctuate substantially, and that they will
continue to do so in the future :

o     The status of our products in development.

o     The formation or termination of our corporate alliances.

o     Determinations regarding our patent applications and those of others.

o     Variations in our quarterly operating results.

      Also, the stock market has recently experienced extreme price and volume
fluctuations. These fluctuations have especially affected the market price of
the stock of many high technology and healthcare-related companies. Such
fluctuations have often been unrelated to the operating performance of these
companies. Nonetheless, these broad market fluctuations may negatively affect
the market price of our common stock.

Limitations on Net Operating Loss
   Carryforwards

      At December 31, 1997, we had (1) net operating loss carryforwards for
federal income tax purposes of approximately $115,000,000 which expire at
various dates from 2000 through 2012 and (2) research credit carryforwards of
approximately $2,303,000 which expire at various dates from 2001 through 2012.
These "carryforwards" are tax assets which we can use in future years to offset
our federal taxable income and reduce the amount of federal taxes that we are
required to pay in those years. There can be no assurances that the Company will
ever generate income which would enable it to utilize the net operating loss
carryforwards.

      Under Section 382 of the Internal Revenue Code of 1986, as amended, a
company's annual ability to use these carryforwards to offset income and
therefore reduce income tax expense may be limited if that company experiences a
change in ownership of more than 50 percentage points within any three-year
period. Since 1986, we have experienced two such ownership changes. As a result,
we are only permitted to use in any one year $5,159,000 of our available net
operating loss carryforwards that relate to periods before these ownership
changes to offset federal taxable income. Similarly, we are limited in using our
research credit carryforwards related to years before the ownership changes to
offset future federal income tax expense. Accordingly, as a result of these
ownership changes, we may be required to pay more federal income tax in future
years than we would have been required to pay had the ownership changes not
occurred. There can be no assurance that the Company will ever generate income
which would enable it to utilize these net operating loss carryforwards.

Dividend Policy and Restrictions

      We have never paid any cash dividends on our common stock. Our Board of
Directors will decide our future dividend policy based on our results of
operations, financial condition, capital requirements and other circumstances.
We do not anticipate that any dividends will be declared on our common stock in
the foreseeable future. Any earnings which we may earn, other than earnings
which may be used to pay dividends owed to the holder of our Series A Preferred
Stock, will be retained to finance our growth. In addition, the terms of the
Series A Preferred Stock restrict our ability to pay dividends on our stock. See
"Prospectus-Summary--The Company--BEC2 Cancer Vaccine" and "Risk
Factors--Dilution."

Year 2000.

   
      We have completed a review of our internal computer systems and we are in
the process of making inquiries of groups with which we do business with respect
to their computer systems, to determine whether these systems will experience a
"Year 2000 problem". A Year 2000 problem would result from a computer system
recognizing the first two digits of a year after the year 1999 as "19" instead
of "20", thereby reading the wrong year. We expect to have identified and
replaced or corrected all computer systems which would cause a Year 2000 problem
by the first quarter of 1999. There 
    


                                       15
<PAGE>

   
is no assurance that we will be able to successfully do this, or that the groups
with which we do business will timely identify and replace their computer
systems which would cause a Year 2000 problem. The failure to identify and
remedy Year 2000 problems could disrupt important operations which could affect
the development and ultimate marketing of potential products as well as put us
at a competitive disadvantage relative to companies that have corrected such
problems.
    

                          -----------------------------

                                 USE OF PROCEEDS

                          -----------------------------

      We will not receive any proceeds from the sale by the Selling Stockholders
of the Shares. They will receive all such proceeds. However, the Selling
Stockholders will pay us the purchase price for the Shares when they exercise
their warrants. If all Selling Stockholders exercised all of their warrants that
they have not yet exercised, we would receive total proceeds of about
$1,127,250. We expect to use any such proceeds (1) to continue to pay for and
expand our research and development programs and (2) for general corporate
purposes, including working capital. There can be no assurance that the Selling
Stockholders will exercise any of their warrants.


                                       16
<PAGE>

                          -----------------------------

                              SELLING STOCKHOLDERS

                          -----------------------------

      The table below presents the following information about the number of
shares of our common stock owned by the Selling Stockholders: (1) the number of
shares such Selling Stockholder beneficially owns as of the date of this
prospectus, (2) the number of Shares that such Selling Stockholder is offering
under this prospectus, (3) the number of shares that such Selling Stockholder
will beneficially own after the completion of this offering and (4) the
percentage of our outstanding shares of common stock that such Selling
Stockholder will beneficially own after the completion of the offering.

      Dr. Harlan W. Waksal is our Executive Vice President and Chief Operating
Officer and is a member of our Board of Directors. Dr. Samuel D. Waksal is our
President and Chief Executive Officer and a member of our Board of Directors.
Dr. Samuel D. Waksal and Dr. Harlan W. Waksal are brothers. Mr. John B. Landes
is our Vice President-Business Development and General Counsel. Dr. Zvi Fuks is
a member of our Scientific Advisory Board. Mr. Robert F. Goldhammer is the
Chairman of our Board of Directors.

<TABLE>
<CAPTION>

                                                                                         Percentage of
                                                                Number of Shares To  Outstanding Shares To
                           Number of Shares   Number of Shares     Be Owned After        Be Owned After
                             Beneficially     Offered By This        Completion          Completion of
 Selling Stockholder(1)        Owned(1)        Prospectus(2)       of Offering(3)          Offering(3)
- ------------------------       --------        -------------       --------------          -----------
<S>                         <C>                  <C>                 <C>                      <C> 
Samuel D. Waksal            1,470,583(4)         431,997(4)          1,038,586                3.8%
Harlan W. Waksal            1,245,780(5)         734,500(5)            511,280                1.9%
Robert F. Goldhammer          836,576(6)         418,000(6)            418,576                1.6%
John B. Landes                337,000(7)         135,000(7)            202,000                 *
Zvi Fuks                      116,500(8)          12,000(8)            104,000                 *
</TABLE>
- --------------------
*     Less than 1%.

(1)   Assumes that all options or warrants to purchase shares of our common
      stock held by the Selling Stockholders are exercisable within 60 days of
      the date of this prospectus.

(2)   Assumes that the Selling Stockholders would currently be allowed to
      exercise all of their warrants to purchase all of the Shares offered by
      this prospectus.

   
(3)   Assumes that the Selling Stockholders have sold all of the Shares offered
      by this prospectus and that all options or warrants to purchase shares of
      our common stock held by them are exercisable within 60 days. Because the
      Selling Stockholders may sell the shares offered by this prospectus from
      time to time, we do not currently know the date of the completion of the
      offering. Therefore, the number and percentages of shares included are
      based on 24,512,107 shares, the total number of our shares of common stock
      outstanding as of December 31, 1998, giving effect to the exercise of all
      of the Selling Stockholders' warrants to purchase Shares offered by this
      prospectus. Shares of our Series A Convertible Preferred Stock are not
      included, because such shares carry no voting rights.
    

(4)   Includes an aggregate of 431,997 Shares previously acquired by Dr. Waksal
      upon the exercise of warrants.

(5)   Includes (i) an aggregate of 337,500 Shares subject to warrants issued to
      Dr. Waksal and (ii) an aggregate of 397,000 Shares previously acquired by
      Dr. Waksal upon the exercise of warrants.

(6)   Includes (i) an aggregate of 120,000 Shares previously acquired by Mr.
      Goldhammer upon the exercise of warrants and (ii) an aggregate of 298,000
      Shares subject to warrants issued to Mr. Goldhammer. The additional shares
      of our common stock listed under the column "Number of Shares Beneficially
      Owned" include 13,314 shares of our common stock held in trust, as to
      which Mr. Goldhammer disclaims beneficial ownership.

(7)   Includes (i) 31,000 Shares previously acquired by Mr. Landes upon the
      exercise of warrants and (ii) 104,000 Shares subject to warrants issued to
      Mr. Landes.

(8)   Includes 12,000 Shares subject to warrants issued to Dr. Fuks.


                                       17
<PAGE>

                          -----------------------------

                              PLAN OF DISTRIBUTION

                          -----------------------------

Manner of Sales; Broker-Dealer Compensation

      The Selling Stockholders may sell any Shares that they acquire when they
exercise their warrants using this prospectus. The Selling Stockholders may
elect to sell any such Shares in privately negotiated transactions or in the
over-the-counter market through brokers and dealers. Such brokers and dealers
may act as agent or as principals. They may receive compensation in the form of
discounts, concessions or commissions from the Selling Stockholders or from the
purchasers of their Shares for whom the broker-dealers may act as agent or to
whom the broker-dealers may sell as principal, or both. The Selling Stockholders
may also sell the shares in reliance upon Rule 144 under the Securities Act of
1933, as amended, at such times as they are eligible to do so. We have been
advised by the Selling Stockholders that they have not made any arrangements for
the distribution of the Shares. Broker-dealers who effect sales for the Selling
Stockholders may arrange for other broker-dealers to participate. Broker-dealers
engaged by the Selling Stockholders will receive commissions or discounts from
them in amounts to be negotiated prior to the sale.

Filing of Supplement to Prospectus In Certain
  Instances

      If any Selling Stockholder notifies us that he or she has entered into a
material arrangement (other than a customary brokerage account agreement) with a
broker or dealer for the sale of Shares under this prospectus through a block
trade, purchase by a broker or dealer or similar transaction, we will file a
supplement to the prospectus under Rule 424(c) under the Securities Act of 1933,
as amended. Such a supplement will disclose:

o     The name of each such broker-dealer.

o     The number of Shares involved.

o     The price at which those Shares were sold.

o     The commissions paid or discounts or concessions allowed to such broker
      dealer(s).

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

o     Any other facts material to the transaction.

Certain Persons Deemed to be Underwriters

      The Selling Stockholders and any broker-dealers who execute sales for them
may be deemed to be "underwriters" within the meaning of the Securities Act of
1933, as amended, because of the number of Shares to be sold or resold by such
persons or entities or the manner of sale of such Shares, or both. If a Selling
Stockholder or any broker-dealer or other holders were determined to be
underwriters, any discounts, concessions or commissions received by them or by
brokers or dealers acting on their behalf and any profits received by them on
the resale of their Shares might be deemed to be underwriting discounts and
commissions under the Securities Act of 1933, as amended.

Regulation M

      The Selling Stockholders have represented to us that any purchase or sale
of Shares by them will comply with Regulation M promulgated under the Securities
Exchange Act of 1934, as amended. In general, Rule 102 under Regulation M
prohibits any person connected with a distribution of our common stock (a
"Distribution") from directly or indirectly bidding for, or purchasing for any
account in which he or she has a beneficial interest, any of our common stock or
any right to purchase our common stock, for a period of one business day before
and after completion of his or her participation in the distribution (we refer
to that time period as the "Distribution Period").

      During the Distribution Period, Rule 104 under Regulation M prohibits the
Selling Stockholders and any other persons engaged in the Distribution from
engaging in any stabilizing bid or purchasing our common stock except for the
purpose of preventing or retarding a decline in the open market price of our
common stock. No such person may effect any stabilizing transaction to
facilitate any offering at the market. Inasmuch as the Selling Stockholders will
be reoffering and reselling our common stock at the market, Rule 104 prohibits
them from effecting any stabilizing transaction in contravention of Rule 104
with respect to our common stock.

                          -----------------------------

                                  LEGAL MATTERS

                          -----------------------------

      Kaye, Scholer, Fierman, Hays & Handler, LLP will issue an opinion about
the validity of the shares for us.


                                       18
<PAGE>

                          -----------------------------

                      DISCLOSURE OF COMMISSION POSITION ON
                 INDEMNIFICATION FOR SECURITIES ACT LIABILITIES

                          -----------------------------

      ImClone's Certificate of Incorporation and Bylaws provide for
indemnification of officers and directors in instances, among others, in which
they acted in good faith and in a manner they reasonably believed to be in, or
not opposed to, our best interests and in which, with respect to criminal
proceedings, they had no reasonable cause to believe their conduct was unlawful.

      Insofar as indemnification for liabilities arising under the Securities
Act of 1933 may be permitted to directors, officers and controlling persons of
ImClone pursuant to the foregoing provisions, or otherwise, we have been advised
that, in the opinion of the Securities and Exchange Commission, such
indemnification is against public policy as expressed in the Securities Act of
1933, as amended, and is, therefore, unenforceable.


                                       19
<PAGE>

                                     PART II
                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.

      The following table sets forth all expenses payable by ImClone in
connection with the sale of the shares offered by this prospectus.

   
         SEC Registration Fee:                                   $  4,328
         Blue Sky Fees and Expenses*:                               1,000
         Legal Fees and Expenses*:                                 35,000
         Accounting Fees and Expenses*:                             5,000
         Miscellaneous*:                                            2,672
                                                                ---------
                Total*:                                           $48,000
    
- -----------------
* Estimated.

Item 15. Indemnification of Directors and Officers.

      Our Certificate of Incorporation and Bylaws set forth the extent to which
our officers and directors may be indemnified by us against any liabilities
which they may incur. The general effect of such provisions is that, on the
terms and conditions set forth in our Certificate of Incorporation and Bylaws,
any person made a party or threatened to be made a party to an action, suit or
proceeding by reason of the fact that he or she is or was a director or officer,
or is or was serving as a director, officer, employee or agent of another
corporation or other enterprise at our request, shall be indemnified by us
against expenses (including attorneys' fees, judgments, fines and amounts paid
in settlement) reasonably incurred or suffered by him or her in connection with
such action, suit or proceeding, to the full extent permitted under the laws of
the State of Delaware; provided, however, that, subject to certain limited
exceptions, we shall indemnify any such person seeking indemnification in
connection with a proceeding initiated by such person only if such proceeding
was authorized by our Board of Directors. Our Certificate of Incorporation gives
our Board of Directors the authority to extend such indemnification to our
employees and other agents as well.

      The general effect of the indemnification provisions contained in Section
145 of the General Corporation Law of the State of Delaware (the "DGCL") is as
follows: A director or officer who, by reason of such directorship or
officership, is involved in any action, suit or proceeding (other than an action
by or in the right of the corporation) may be indemnified by the corporation
against expenses (including attorneys' fees), judgments, fines and amounts paid
in settlement actually and reasonably incurred by him or her in connection with
such action, suit or proceeding if he or she acted in good faith and in a manner
he or she reasonably believed to be in or not opposed to the best interests of
the corporation, and, with respect to any criminal action or proceeding, has no
reasonable cause to believe that his or her conduct was unlawful. A director or
officer who, by reason of such directorship or officership, is involved in any
action or suit by or in the right of the corporation may be indemnified by the
corporation against expenses (including attorneys' fees) actually and reasonably
incurred by him or her in connection with the defense or settlement of such
action or suit if he or she acted in good faith and in a manner he or she
reasonably believed to be in or not opposed to the best interests of the
corporation, except that no indemnification may be made in respect of any claim,
issue or matter as to which he or she shall have been adjudged to be liable to
the corporation unless and only to the extent that a court of appropriate
jurisdiction shall approve such indemnification.

      Our Certificate of Incorporation provides that, to the maximum extent
permitted under the DGCL, a director of ImClone shall not be personally liable
to us or to any of our stockholders for monetary damages for breach of fiduciary
duty as a director of ImClone. Section 102(b)(7) of the DGCL permits a
corporation to include in its certificate of incorporation a provision that
eliminates or limits the personal liability of a director to the corporation or
its stockholders for monetary damages for breach of fiduciary duty as a
director; provided, that such provision shall not eliminate or limit the
liability of a director (i) for any breach of the director's duty of loyalty to
the corporation or its stockholders, (ii) for acts or omissions not in good
faith or which involve intentional misconduct or a knowing violation of law,
(iii) under Section 174 of the DGCL or (iv) for any transaction from which the
director derived in improper personal benefit.

Item 16. Exhibits.

   
Exhibit No.   Description
- -----------   -----------

5.1         Opinion of Kaye, Scholer, Fierman, Hays & Handler, LLP regarding the
            legality of the securities being registered. *

10.70       Development and License Agreement between the Company and Merck KGaA
            dated December 14, 1998. **
    


                                       20
<PAGE>

   
23.1        Consent of KPMG LLP.***

23.2        Consent of Kaye, Scholer, Fierman, Hays & Handler, LLP. (Included in
            Exhibit 5.1).

*           Previously Filed
**          Filed  herewith.  Confidential  Treatment  has been  requested  with
            respect to certain portions of this Exhibit.
***         Filed herewith.
    

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 this 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 this 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 Commission 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 this Registration
            Statement or any material change to such information in this
            Registration Statement;

provided, however, that paragraphs (a)(1)(i) and (a)(1)(ii) above 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
Commission 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
      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; and

            (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 the offering.

      (b) 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 of 1934) 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) 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 Securities and
Exchange Commission 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.

      (d) The undersigned registrant hereby undertakes that:

            (1) For purposes of determining any liability under the Securities
      Act of 1933, the information omitted from the form of prospectus filed as
      part of this registration statement in reliance upon Rule 430A and
      contained in a form of 


                                       21
<PAGE>

prospectus filed by the registrant pursuant to Rule 424(b)(1) or (4) or 497(h)
under the Securities Act shall be deemed to be part of this registration
statement as of the time it was declared effective.

            (2) For the purpose of determining any liability under the
      Securities Act of 1933, each post-effective amendment that contains a form
      of prospectus 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.


                                       22
<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 New York, State of New York, on the 8th day of
January 1999.
    

                                     IMCLONE SYSTEMS INCORPORATED

                                     By:  /s/ Samuel D. Waksal
                                          -------------------------------------
                                          Samuel D. Waksal
                                          President and Chief Executive Officer

       

     Signature                            Title                       Date
     ---------                            -----                       ----

   
          *
- --------------------------   Chairman of the Board and Director  January 8, 1999
Robert F. Goldhammer      

          *
- --------------------------   President, Chief Executive Officer  January 8, 1999
Samuel D. Waksal             and Director                           
                             (Principal Executive Officer)

          *
- --------------------------   Executive Vice President, Chief     January 8, 1999
Harlan W. Waksal             Operating Officer and Director          

          *
- --------------------------   Vice President of Finance and       January 8, 1999
Carl Goldfischer             Chief Financial Officer   
                             (Principal Financial and 
                             Accounting Officer)

          *
- --------------------------   Director                            January 8, 1999
Jean Carvais
                                                     
          *
- --------------------------   Director                            January 8, 1999
Vincent T. DeVita, Jr.                                            

          *
- --------------------------   Director                            January 8, 1999
Paul B. Kopperl                                                      

          *
- --------------------------   Director                            January 8, 1999
William R. Miller                                                 

          *
- --------------------------   Director                            January 8, 1999
David M. Kies                                                        

          *
- --------------------------   Director                            January 8, 1999
John Mendelsohn                                                       

          *
- --------------------------   Director                            January 8, 1999
Richard Barth                                                       

/s/ John B. Landes
- --------------------------
John B. Landes
as attorney-in-fact
    


                                      S-1
<PAGE>

                                  EXHIBIT INDEX

Exhibit No.   Description
- -----------   -----------

   
5.1           Opinion of Kaye, Scholer, Fierman, Hays & Handler, LLP regarding
              the legality of the securities being registered.*

10.70         Development and License Agreement between the Company and Merck
              KGaA dated December 14, 1998.**

23.1          Consent of KPMG LLP***

23.2          Consent of Kaye, Scholer, Fierman, Hays & Handler, LLP. 
              (Included in Exhibit 5.1).

*     Previously Filed

**    Filed herewith Confidential Treatment has been requested with respect to
      certain portions of this Exhibit.

***   Filed herewith.
    



                                                                   Exhibit 10.70

                                                CONFIDENTIAL TREATMENT REQUESTED

                        DEVELOPMENT AND LICENSE AGREEMENT

      This Development and License Agreement (this "Agreement"),  dated the 14th
day of December, 1998, by and between:

      ImClone Systems Incorporated, a Delaware corporation, having an address at
180 Varick Street,  New York, New York,  10014 USA  (hereinafter  referred to as
"ImClone"), and

      Merck KGaA, a German corporation with general partners,  having an address
at Frankfurter  Stra(beta)e 250, D-64293 Darmstadt,  Federal Republic of Germany
(hereinafter referred to as "Merck").

                              W I T N E S S E T H :

      WHEREAS,  ImClone is a research-based  corporation having expertise in the
area of biotechnology leading to the development of innovative  biotechnological
products, including the area of cancer therapeutics;

      WHEREAS,  ImClone possesses certain  knowledge,  know-how,  trade secrets,
technical   information,   and  expertise  with  respect  to  the  research  and
development of cancer therapeutics;

      WHEREAS, Merck possesses related know-how and trade secrets and intends to
achieve  a  substantial  business  presence  in  the  area  of  biotechnological
products,  including but not limited to cancer  therapeutics,  and possesses the
capability to evaluate, develop, manufacture and commercialize products for uses
therein;

      WHEREAS, the parties desire to develop, manufacture and commercialize C225
(as  described  in Schedule A,  attached  hereto and  specifically  incorporated
herein);

      WHEREAS,  ImClone has filed or licensed certain patent  applications  with
respect to targeting Epidermal Growth Factor Receptors (sometimes referred to as
"EGFr") in combination with

<PAGE>

chemotherapy and radiotherapy, respectively, as further described in Schedule B,
attached hereto and specifically incorporated herein;

      WHEREAS, Merck desires to develop and commercialize cancer therapeutics as
part of its cancer therapeutics business; and

      WHEREAS,  ImClone  desires  to grant to Merck  and Merck  accepts  certain
rights and  licenses,  all as set forth herein,  under the terms and  conditions
hereinafter set forth;

      NOW,  THEREFORE,  in consideration of the mutual covenants and obligations
hereinafter provided, both parties agree to the following:

                                    ARTICLE I

                                   Definitions

      The following  terms, as used in this  Agreement,  shall have the meanings
set forth in this Article I.

      1.1.  The term  "Acquired  Non-Voting  Shares"  shall mean those shares of
non-voting  securities  of  ImClone,  which  shall be  newly  issued  shares  of
non-voting  securities  of  ImClone,  acquired  by  Merck  upon  making  certain
Milestone Payments under certain  circumstances,  and which shall be convertible
into  shares of Common  Stock as  provided  in Section  4.1(b) and  Schedule  E,
attached hereto and specifically incorporated herein.

      1.2. The term  "Acquired  Voting Shares" shall mean those shares of Common
Stock,  which shall be newly issued  shares of Common  Stock,  acquired by Merck
upon making  certain  Milestone  Payments,  as  provided  in Section  4.1(a) and
Schedule E hereof.

      1.3. The term "Affiliate" shall mean with respect to any Person, any other
Person directly or indirectly controlling, controlled by or under common control
with  such  other  Person.   The  term  "control"  (and  the  derivative   terms
"controlling" and "controlled") as used herein means the possession,

***Confidential Treatment Requested


                                       2
<PAGE>

directly or  indirectly,  of the power to direct or cause the  direction  of the
management  and the policies of a Person,  whether  through  ownership of voting
securities, or by contract or otherwise.

      1.4. The term  "Alternative  Products" shall mean those products which, as
part  of  the  Research  and  Development,  may  be  developed  and/or  acquired
subsequent  to the execution of this  Agreement  solely by ImClone or any of its
Affiliates or jointly with Merck or any of its  Affiliates as an  alternative to
the  Compound,   including  but  not  limited  to  any  inhibitors  of  EGFr  or
improvements thereto that are not the Compound or an Improvement.

      1.5.  The term  "Alternative  Product  Patents"  shall mean any and all of
ImClone's  right,  title and  interest in any patent  application  covering  any
Alternative  Products  and/or  process  for  the  manufacture  or  use  of  such
Alternative  Products,  together with any  divisions,  reissues,  continuations,
continuations-in-part,  extensions,  restorations,  and/or  additions  therefor,
owned,  licensed or otherwise  controlled  individually by ImClone or any of its
Affiliates  or jointly by ImClone or any of its  Affiliates  and Merck or any of
its  Affiliates,  during the term of this Agreement and developed as part of the
Research and Development with respect to Alternative  Products,  and all patents
that may issue from time to time from any such patent applications.

      1.6. The term "Alternative  Product  Technology" shall mean any and all of
ImClone's  right,  title and interest in any technology that is developed and/or
acquired by ImClone or any of its  Affiliates,  or jointly  with Merck or any of
its Affiliates, subsequent to the date of this Agreement and which is reasonably
necessary to enable the making, use or sale of Alternative  Products,  including
but not  limited  to  methods  of  manufacture,  characterization  and  assaying
techniques, biological materials such as compounds, DNA, RNA, plasmids, vectors,
organisms, antibodies, hybridomas, fusion partners, systems for the augmentation
of the  biological  response,  including  but not limited to adjuvants and other
carriers and/or  enhancers,  and processes  employed for producing or developing
Alternative  Products,  purification  methods and methods for using  Alternative
Products.

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                                       3
<PAGE>

      1.7. The term "C225" shall mean the chimerized monoclonal antibody to EGFr
known as C225,  as described  in Schedule A,  attached  hereto and  specifically
incorporated herein.

      1.8.  The term  "Chemotherapy  Patent"  shall mean the  patents and patent
applications  specified in Schedule B as  "Applications  of Schlessinger et al.,
assigned to Rhone Poulenc Rorer."

      1.9.  The  term  "Merck   Products"   shall  mean  any  and  all  products
incorporating  the humanized  antibody of Merck or any of its Affiliates to EGFr
(including  any  improvements  to such  products)  which,  but for the  licenses
granted herein,  would infringe the Chemotherapy  Patent and/or the Radiotherapy
Patent.  

      1.10.  "Merck  Products  Net Sales" shall mean the total  invoiced  amount
related  to all  sales in the  Territory  by Merck and its  Affiliates  of Merck
Products in any form to a Person which is not Merck or an Affiliate of Merck,  a
sublicensee, or an Affiliate of a sublicensee, less the following: 

            (a)  Customary  or  usual  trade  or  quantity  discounts  or  other
      charge-backs actually taken by the customer and not already credited on an
      invoice;

            (b) Sales, use,  value-added or other excise taxes, imposed and paid
      directly with respect to the sale, and included  within the invoice price,
      and separately stated on the invoice;

            (c)  Refunds  for  customer  returns,  not  already  credited  on an
      invoice; and

            (d)  Customs,  duties,  transportation  charges  and  other  similar
      expenses separately invoiced.

      1.11. The term "Collateral  License Agreements" shall mean certain license
agreements, both currently existing and not yet entered into with third parties,
to be negotiated and entered into by ImClone, subject to Section 11.7 hereof, as
more  fully   described  in  Schedule  F,  attached   hereto  and   specifically
incorporated herein.

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                                       4
<PAGE>

      1.12. The term  "Collateral  License  Agreement  Royalties" shall have the
meaning attributed to such term in Section 9.6 hereof.

      1.13. The term "Common Stock" shall mean ImClone's common stock, par value
$0.001 per share.

      1.14. The term  "Compound"  shall mean the monoclonal  antibody  targeting
EGFr developed by ImClone and known as C225, as more  specifically  described in
Schedule  A,  attached  hereto  and  specifically   incorporated  herein.  

      1.15.  "Conversion  Notification Date" shall have the meaning set forth in
Schedule E, attached hereto and specifically incorporated herein.

      1.16.  The term  "Conversion  Triggering  Date" shall have the meaning set
forth in Schedule E, attached hereto and specifically incorporated herein.

      1.17.  The term  "Fully-Loaded  Cost of Goods"  shall have the meaning set
forth in Schedule C, attached hereto and specifically incorporated herein.

      1.18. The term "Gross Margin" shall mean [ *** ] .

      1.19. The term "Improvements"  shall mean all enhancements  ImClone or any
of its  Affiliates  may make to the Compound  prior to the  termination  of this
Agreement, whether or not patentable, which are invented, developed,  discovered
or otherwise acquired by ImClone or any of its Affiliates.

      1.20.  The  term  "Licensed  Product  Patents"  shall  mean any and all of
ImClone's  right,  title and interest in any non-U.S.  and  non-Canadian  patent
application  covering the Compound and/or any Improvement and/or process for the
manufacture or use of the Compound  and/or such  Improvement,  including but not
limited  to,  those set forth in Schedule B,  attached  hereto and  specifically
incorporated  herein, as amended from time to time, together with any divisions,
reissues, continuations, continuations-

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                                       5
<PAGE>

in-part, extensions, restorations, and/or additions therefor, owned, licensed or
otherwise controlled by ImClone or any of its Affiliates during the term of this
Agreement,  and all patents that have issued or that may issue from time to time
from any such patent applications. 

      1.21. The term "Licensed  Products"  shall mean the Compound,  any and all
products  incorporating the Compound and any and all products made by use of any
compound or product covered by any Licensed Product Patent,  including,  but not
limited to, any Improvements to the Compound.

      1.22. The term  "Licensed  Product  Technology"  shall mean any and all of
ImClone's right, title and interest in any technology that is owned, licensed or
otherwise  controlled by ImClone or any of its Affiliates as of the date of this
Agreement,  as well  as any and all  technology  developed  and/or  acquired  by
ImClone or any of its Affiliates during the term of the Agreement,  and which is
reasonably  necessary  to enable the making,  use or sale of Licensed  Products,
including  but not  limited  to  methods of  manufacture,  characterization  and
assaying techniques, biological materials such as compounds, DNA, RNA, plasmids,
vectors,  organisms,  antibodies,  hybridomas,  fusion partners, systems for the
augmentation of the biological response,  including but not limited to adjuvants
and other carriers  and/or  enhancers,  and processes  employed for producing or
developing the Compound and/or Licensed Products, purification methods, Licensed
Products per se, and methods for using Licensed Products.

      1.23.  The  term  "Loss"  means,  with  respect  to  the   indemnification
provisions  set  forth in  Article  X,  any and all  damages,  claims,  demands,
liabilities,  losses, costs or expenses of any kind, including,  but not limited
to, all costs and expenses of  investigating  or defending any claims,  demands,
liabilities or losses, and reasonable  attorneys' fees and litigation  expenses.

      1.24.  The term  "Manufacturing  Facility  Line of Credit"  shall have the
meaning attributed to such term in Section 4.9.

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                                       6
<PAGE>

      1.25. The term "Milestone" shall have the meaning  attributed to such term
in Schedule E, attached hereto and specifically incorporated herein.

      1.26. The term  "Milestone  Conversion  Shares" shall have the meaning set
forth in Schedule E attached hereto and specifically incorporated herein.

      1.27. The term  "Milestone  Payment" shall have the meaning  attributed to
such term in Section 4.1 hereof.

      1.28. The term "Milestone  Payment Date" shall have the meaning attributed
to such term in Section 4.1 hereof.  1.29.  The term "Net Sales"  shall mean the
total  invoiced  amount  related  to all  sales by Merck and its  Affiliates  of
Licensed  Products and  Alternative  Products in any form to any Person which is
not  Merck,  an  Affiliate  of  Merck,  a  sublicensee  or  an  Affiliate  of  a
sublicensee, less the following:

            (a)  Customary  or  usual  trade  or  quantity  discounts  or  other
      charge-backs actually taken by the customer and not already credited on an
      invoice;

            (b) Sales, use,  value-added or other excise taxes, imposed and paid
      directly with respect to the sale, and included  within the invoice price,
      and separately stated on the invoice; ]

            (c)  Refunds  for  customer  returns,  not  already  credited  on an
      invoice; and

            (d)  Customs  duties,   transportation  charges  and  other  similar
      expenses separately invoiced.

      1.30.  The term "Person" means an  individual,  corporation,  partnership,
limited liability company,  association,  trust or other entity or organization,
including a government or political  subdivision or an agency or instrumentality
thereof.

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                                       7
<PAGE>

      1.31. The term  "Preferred  Stock Purchase  Agreement"  means that certain
Preferred Stock Purchase Agreement, dated as of December 3, 1997, by and between
ImClone and Merck.

      1.32. The term  "Radiotherapy  Patent" shall mean the patent  applications
specified in Schedule B as "Applications of Waksal et al., assigned to ImClone."

      1.33.  The term  "Research  and  Development"  shall  mean that work which
ImClone and Merck  undertake to conduct in connection  with  Licensed  Products,
and,  to the  extent  applicable,  Alternative  Products,  as set  forth  in the
Research and Development Protocol.

      1.34. The term "Research and Development Protocol" shall mean the plan for
the conduct of the  Research and  Development  during the period of Research and
Development,  as set forth in  Schedule  D,  attached  hereto  and  specifically
incorporated herein, and as may be amended by the parties from time to time.

      1.35.  The term  "Series A  Convertible  Preferred  Stock"  shall mean the
Series A Convertible Preferred Stock of ImClone, $1.00 par value per share.

      1.36. The term "Standstill Period" shall mean the time period beginning on
the date of this Agreement and terminating on the fifth (5th) anniversary of the
Preferred Stock Purchase Agreement, i.e. December 3, 2002.

      1.37. The term "Steering Committee" shall mean the committee as defined in
Section 3.1.

      1.38. The term "Territory" shall mean worldwide, excluding the Dominion of
Canada  and  the  United  States  of  America  (including  all  territories  and
possessions thereof).

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                                       8
<PAGE>

                                   ARTICLE II

                                 Grant of Rights

      2.1.  Subject to Section 2.3,  ImClone hereby grants to Merck an exclusive
license with the right to sublicense as limited by Section 2.6, to make, use and
sell  Licensed  Products and  Alternative  Products  within the  Territory and a
non-exclusive license to use Licensed Product Technology and Alternative Product
Technology for the manufacture of the Compound.

      2.2.  ImClone  hereby  grants to Merck an exclusive  license,  without the
right to sublicense  other than to Merck's  Affiliates or to  sublicensees  with
ImClone's  prior  written  consent,  which  consent  shall  not be  unreasonably
withheld, the Radiotherapy Patent and the Chemotherapy Patent, respectively,  to
make, use and sell Merck  Products  within the Territory for a term beginning on
the  date  of  this  Agreement  and  continuing   throughout  the  life  of  the
Radiotherapy Patent and of the Chemotherapy Patent, respectively,  in each case,
as such patent may be extended or restored. In the event that the Compound fails
in the United States and Canada ("Product Failure"),  then the exclusive license
granted under this Section 2.2 shall automatically  become a worldwide exclusive
license granted to Merck for a term beginning on the date of the Product Failure
and  continuing  throughout  the  life of the  Radiotherapy  Patent  and/or  the
Chemotherapy  Patent,  as the case may be, in each case,  as such  patent may be
extended or restored.  This  Section 2.2 shall  survive the  termination  of the
Agreement.

      2.3.  The parties  hereby  agree to use their best  reasonable  efforts to
reach a separate  agreement  within  twelve (12) months of the first  commercial
sale of any  Licensed  Product  in the  Territory  pursuant  to which  Merck and
ImClone  will   collaboratively   develop  and  market  Licensed   Products  and
Alternative Products in Japan;  provided,  however, that if no such agreement is
reached within such  twelve-month  period,  the parties shall have  co-exclusive
rights with the right to  sublicense  with respect to Licensed  Products  and/or
Alternative  Products  in Japan.  Notwithstanding  any other  provision  of this
Agreement,   ImClone  acknowledges  and  agrees  that  ImClone  shall  under  no
circumstances  take any unilateral  action

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                                       9
<PAGE>

with respect to any Licensed Products
and/or Alternative Products in Japan without Merck' prior written consent, which
consent shall not be unreasonably withheld.

      2.4. Notwithstanding any other provision of this Agreement, if at any time
during  the  term of this  Agreement  ImClone  determines  to  grant a  license,
exclusive or  otherwise,  to make,  have made,  use,  sell or have sold Licensed
Products or Alternative Products outside the Territory (not including a right to
distribute),  it shall so notify Merck in writing.  Merck shall have thirty (30)
calendar days from the receipt of such written notification to notify ImClone in
writing of its desire to negotiate for such a license.  Should Merck make such a
written  notification,  then for a period of sixty (60) calendar days therefrom,
the parties  shall  negotiate in good faith the terms of such a license.  Should
the parties not consummate a license in this period of sixty (60) calendar days,
the offer to Merck shall be deemed formally withdrawn and ImClone shall have the
right to  negotiate  and  consummate  a license  with a third  party;  provided,
however,  that ImClone shall not consummate such a license with such third party
unless  the  terms of such  license  offered  to such  third  party  are no more
favorable  than the terms  previously  offered to Merck.  If such terms,  in the
aggregate,  are more favorable than the terms previously  offered to Merck, then
ImClone, by written notice, shall offer such terms to Merck and Merck shall have
fifteen (15) calendar days from  ImClone's  notice in which to accept such offer
and consummate such license.

      2.5. To the fullest  extent  permitted by law, any license  granted herein
shall extend for a term  beginning  on the date of this  Agreement  and,  unless
terminated  sooner as herein provided,  shall, in the case of Licensed  Products
sold  under  Licensed  Product  Patents  and  Alternative  Products  sold  under
Alternative Product Patents,  continue throughout the life of the last-to-expire
patent included in Licensed Product Patents or Alternative  Product Patents,  as
the  case  may be,  in  each  case,  as such  Licensed  Product  Patents  and/or
Alternative  Product  Patents  may be extended  or  restored,  or in the case of
Licensed  Products or Alternative  Products that incorporate or utilize Licensed
Product  Technology  or  Alternative  Product  Technology,  as the  case may be,
continue as a  royalty-bearing  license for fifteen  (15) years from the date of
first  commercial  sale of a Licensed  Product,  as the case may be, after which
time the licenses  

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                                       10
<PAGE>

under Licensed Product Technology or Alternative Product Technology, as the case
may be, shall survive  without further royalty payment and shall be irrevocable,
except that the licenses shall become nonexclusive.

      2.6. Merck shall have the right to sublicense the manufacture  and/or sale
of Licensed  Products  and/or  Alternative  Products,  provided  Merck  notifies
ImClone in writing of any such  sublicense,  and continues to fulfill all of its
material obligations  contained in this Agreement,  including but not limited to
the payment of all royalties,  keeping of records,  and reporting of sales;  and
further  provided,  however,  that Merck  shall not so  sublicense  without  the
consent of ImClone and ImClone  shall have the right to withhold  its consent to
any such  sublicensee  and  sublicense,  which consent shall not be unreasonably
withheld.  Notwithstanding any other provision of this Agreement, the respective
rates of royalties payable to ImClone on sales of Licensed Products, Alternative
Products and Merck Products in the Territory by Merck's  sublicensees  and their
Affiliates  shall be calculated in a manner mutually agreed by the parties.  Any
sublicense  agreement shall contain terms  obligating the sublicensee to provide
and make available its books and records  pursuant to Article V hereunder and to
comply with the  confidentiality  provisions of Article VI and the  restrictions
set forth at Section 9.7, Section 9.10 and Section 9.11.

      2.7. Under no circumstances shall this Agreement be construed to grant any
right or license other than those rights or licenses  expressly  granted in this
Article II. Any other right or license shall be evidenced by a separate  written
license agreement between Merck and ImClone,  executed by both parties.  ImClone
and Merck hereby  specifically  reserve all rights to their respective  patents,
technology, products, and any other applicable information not licensed herein.

      2.8. With the exception of [ *** ] for research purposes and those matters
described in Schedule  2.8,  ImClone shall not for a period of [ *** ] after the
execution of this Agreement [ *** ]. 

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                                       11
<PAGE>

                                  ARTICLE III

                            Research and Development

      3.1. In order to  establish a fruitful  cooperation  between the  parties,
immediately  after the execution of this  Agreement,  the parties shall exchange
know-how (Merck) and Licensed Product Technology  (ImClone) relating to Licensed
Products.  Merck and ImClone  shall  conduct  Research  and  Development  toward
commercialization of Licensed Products and, if applicable, Alternative Products,
in the Territory,  in accordance with the Research and Development Protocol. The
Research and  Development  shall be reviewed and defined on a regular basis,  at
least quarterly, by a committee consisting of two representatives from Merck and
two representatives from ImClone (the "Steering Committee").

      3.2.  Meetings  of  the  Steering   Committee  shall  be  chaired  by  one
responsible  person  (project  leader)  from  each of  ImClone  and  Merck in an
alternating manner. Each party shall have one vote. The project leader of either
party shall have the power fully to represent the position of his or her company
and the  decisions  of his or her  company's  management.  In  case a  unanimous
decision  cannot be reached,  the  principal  executive  officers of ImClone and
Merck or their designees shall use reasonable  efforts to resolve the dispute in
good faith.

      3.3.  Meetings of the Steering  Committee shall be held at least quarterly
and at such  times  as  shall  be  necessary  or  useful  for the  Research  and
Development  contemplated herein and as shall be agreed upon between the parties
hereto.  Additional  persons,  including  persons  from each party  representing
different  developmental   functions,   may  attend  meetings  of  the  Steering
Committee,  without voting rights,  at the invitation of the respective  project
leaders.

      3.4. The Steering  Committee shall be responsible  for: 

            (1)  establishing,  supplementing  and  modifying  the  Research and
      Development Protocol from time to time;

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            (2)  defining  the  goals  and  time  frames  of  the  Research  and
      Development Protocol; and

            (3) allocating tasks and costs and coordinating  activities required
      to carry out the tasks laid down in the Research and Development Protocol.

      Through the Steering Committee,  to the extent permitted by any applicable
law,  including but not limited to antitrust and  competition  laws, the parties
shall consult with each other concerning commercialization strategies, including
but not limited to pricing of Licensed Products and Alternative  Products within
the Territory;  provided,  however, that Merck shall have the right to determine
at its sole discretion all prices of Licensed Products and Alternative  Products
sold within the Territory.

      3.5.  Both parties shall report at least  semi-annually,  or at such other
times as the  Steering  Committee  shall  determine,  any and all  Research  and
Development  activities  to the  Steering  Committee  in writing.  Such  written
reports shall contain,  among other things, all information relevant to enabling
Merck to enter into and conduct human clinical studies in the Territory.

      3.6. The Research and Development  Protocol includes,  or may include, the
conduct  and  management  of  clinical  trials and the  filing  for  appropriate
regulatory  approvals  for the sale of the  Licensed  Products  and  Alternative
Products, as applicable, in the Territory. Each party hereby agrees to share all
data generated in its respective territory with respect to Licensed Products and
Alternative  Products for the support of any regulatory  submissions  related to
Licensed  Products and Alternative  Products to any government  authority by the
other party.  Each party further  agrees to use its  reasonable  best efforts to
design studies  (including  design with respect to implementation of studies and
collection of data from studies) in cooperation with the other party in order to
expedite regulatory approvals in each such territory.  The parties further agree
that:

            (a) All such clinical trials and regulatory efforts in the Territory
      shall be the sole responsibility of Merck and shall be coordinated through
      the Merck regulatory group.  Merck shall cause all necessary  governmental
      approvals to be filed in the Territory.

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            (b) All such  clinical  trials and  regulatory  efforts  outside the
      Territory  shall  be the  sole  responsibility  of  ImClone  and  shall be
      coordinated through the ImClone regulatory group.  ImClone shall cause all
      necessary governmental approvals to be filed outside the Territory.

            (c) The  respective  responsibilities  and costs of the parties with
      respect to clinical trials,  regulatory efforts and filing of applications
      for necessary  governmental approvals in Japan shall be negotiated in good
      faith and set forth in a separate  written  agreement or agreements by and
      between the parties as contemplated in Section 2.3 hereof.


      3.7.  Licensed  Product  Technology and  Alternative  Product  Technology,
including,  but not limited to,  Licensed  Products  and  Alternative  Products,
delivery   formulations   for  Licensed   Products  and  Alternative   Products,
experimental,  pre-clinical and clinical trial data, regulatory submissions with
all back-up  (including a right of reference to such  submissions) in connection
with Licensed  Products and Alternative  Products,  shall be freely available to
Merck in the Territory and ImClone outside the Territory in a manner  consistent
with the rights  and  obligations  of the  parties  hereunder.  In the case of a
termination resulting in a reversion of rights under Section 11.8 to an original
licensor,  the  parties  shall,  to the  extent  permitted  by  applicable  law,
negotiate in good faith to reach an agreement with usual and customary terms for
similar  agreements under comparable  circumstances  providing for access and/or
transfer of  ownership,  as necessary to all  necessary  regulatory  filings and
supporting  documentation  and data related to application  for approval to sell
Licensed Products or Alternative Products.

      3.8.   ImClone  shall  supply  and  Merck  shall   purchase  from  ImClone
manufactured  Licensed  Products  and  Alternative  Products  for the conduct of
clinical   trials   and   commercialization   in   the   Territory.   Prior   to
commercialization,  ImClone shall use its best reasonable  commercial efforts to
supply Licensed Products or Alternative  Products,  as the case may be, to Merck
in the quantities  reasonably  requested by Merck. ImClone shall supply all such
Licensed  Products and  Alternative  Products for use in the conduct of clinical
trials at a price equal to the  Fully-Loaded  Cost of Goods.  The parties  shall
negotiate and enter 

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into separate  supply  agreements,  with usual and  customary  terms for similar
agreements under comparable  circumstances,  which provide for (a) the supply to
Merck for the  commercialization  of  Licensed  Products at a price equal to the
Fully-Loaded Cost of Goods and (b) the supply to Merck for the commercialization
of each Alternative Product at a price equal to the Fully-Loaded Cost of Goods.

                                   ARTICLE IV

                  Milestone Payments; Royalties; Line of Credit

      4.1. For good and valuable consideration,  including,  but not limited to,
the licenses granted by ImClone to Merck herein, the research to be performed by
ImClone in connection with the Research and  Development,  and the technology to
be  transferred in connection  with those  licenses and said  research,  ImClone
shall be compensated  by means of certain  milestone  payments,  as specified on
Schedule E, attached hereto and specifically incorporated herein (the "Milestone
Payments").  The date on which any given Milestone Payment is due and payable is
referred to in this Agreement as a "Milestone Payment Date."

            (a) Subject to Section  4.1(b)  hereof,  upon the payment of certain
      Milestone  Payments,  as provided in Schedule E,  ImClone  shall issue and
      deliver to Merck, or to an Affiliate or Affiliates of Merck  designated by
      Merck, Acquired Voting Shares at a purchase price calculated in the manner
      specified  in  Schedule  E.  The  parties   acknowledge   and  agree  that
      notwithstanding  any other provision of this Agreement,  ImClone shall not
      be obligated  during the Standstill  Period to issue  additional  Acquired
      Voting  Shares  to  Merck  if such  issuance  would  cause  the  aggregate
      beneficial   ownership  of  Common  Stock  of  Merck  and  its  Affiliates
      (including  all shares of Common Stock that Merck and its  Affiliates  may
      have the right to acquire as of the relevant  Milestone  Payment Date upon
      the  conversion  of the Series A  Convertible  Preferred  Stock) to exceed
      19.9% of the total  outstanding  shares of Common Stock on a primary basis
      as of the relevant Milestone Payment Date.

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            (b) In the event  Merck is  prohibited  at any time  from  receiving
      Acquired Voting Shares due to the operation of Section 4.1(a) above,  then
      ImClone  shall  issue to Merck in the manner  specified  in Schedule E, in
      lieu of such  Acquired  Voting  Shares,  an amount of Acquired  Non-Voting
      Shares equal to the number of Acquired Voting Shares that Merck would have
      acquired but for the operation of this Section  4.1(b) at a purchase price
      equal to the purchase  price that would have been  applicable  to Acquired
      Voting  Shares  delivered on such  Milestone  Payment  Date.  The Acquired
      Non-Voting  Shares  shall have no voting  rights and shall be  convertible
      into shares of Common Stock on a  share-per-share  basis,  as described in
      Schedule E; in all other respects,  the Acquired  Non-Voting  Shares shall
      have terms identical to those of shares of Common Stock. 

            (c) With  respect  to all  Registrable  Securities  (as  defined  in
      Schedule G hereof),  Merck shall have the registration rights set forth in
      the  registration  rights  agreement  appended  hereto as  Schedule G, and
      specifically incorporated herein. This Section 4.1(c) and Schedule G shall
      survive the termination of the Agreement.

            (d) If at any time  during  the term of this  Agreement  stockholder
      approval is  necessary  for the issuance of any  Acquired  Voting  Shares,
      Acquired Non-Voting Shares or Milestone  Conversion Shares to Merck or its
      Affiliates  pursuant  to  this  Agreement,  ImClone  shall  use  its  best
      reasonable  efforts  to  obtain  such  stockholder  approval  as  soon  as
      practicable.

            (e) Nothing in this  Section 4.1 shall  require  ImClone to take any
      action in connection with the issuance of any of its securities that would
      contravene (or subject  ImClone to de-listing of any of its securities for
      failure to satisfy all  requirements  under) the rules and  regulations of
      any exchange or quotation system on which ImClone's  securities are listed
      or quoted  including,  but not limited to,  Section  4460(i)(1)(D)  of the
      Marketplace Rules of the National Association of Securities Dealers.  

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      4.2.  Merck  shall pay  ImClone  royalties  quarterly  on (i) sales in the
Territory  by  Merck  and  its  Affiliates  of (A)  Licensed  Products  and  (B)
Alternative  Products  developed  and/or  acquired  by  ImClone  or  any  of its
Affiliates  and (ii) sales in the Territory,  subject to Section 2.2 hereof,  by
Merck and its Affiliates of Merck Products as follows:

            (a) Merck  shall pay ImClone a royalty of [***] of [***] of Licensed
      Products sold in the Territory on the first [***];

            (b) Merck  shall pay ImClone a royalty of [***] of [***] of Licensed
      Products sold in the Territory in excess of [ *** ];

            (c) Merck  shall pay ImClone [ *** ], on sales in the  Territory  of
      Alternative  Products  developed  and/or acquired by ImClone or any of its
      Affiliates;  provided, however, that such amount shall not exceed [***] of
      [ *** ]; and

            (d) Merck shall pay ImClone a royalty of [***] of [ *** ].

      4.3.  Within  thirty  (30)  calendar  days after the first day of January,
April,  July and October in each year during the term of this  Agreement,  Merck
shall prepare a written report setting forth for the preceding  fiscal  quarter,
on a country-by-country and  product-by-product  basis, such of the following as
may be applicable under the royalty payment provisions of this Article IV:

            (i) the [ *** ] and [ *** ] of all Licensed Products and Alternative
      Products  sold by Merck  and its  Affiliates  and  sublicensees  and their
      Affiliates under this Agreement;

            (ii) the Merck  Products  Net  Sales;  

            (iii) the amount of royalty payments; and

            (iv) any other information reasonably necessary to show the basis on
      which such payment has been computed.

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      4.4. Each payment  report  rendered shall be accompanied by the payment by
wire transfer of all royalty payments due for the fiscal quarter in question.

      4.5. All payments due under this Article IV shall be paid in U.S.  dollars
in immediately  available  funds by wire transfer to a bank account in New York,
N.Y., USA designated by ImClone.  For purposes of computing the royalty payments
on products sold outside the United States, such royalty payments first shall be
determined  in the currency in which such  products are sold and then  converted
into the equivalent in U.S.  dollars at the selling rate for the last day of the
quarter as reported in The Wall Street Journal (Eastern Edition).

      4.6. With regard to the royalty  obligations  contemplated in this Article
IV, products shall be deemed to have been sold when billed or shipped, whichever
shall first occur, in an arm's-length  transaction with a buyer. If the buyer is
an Affiliate of Merck that resells  products,  products  shall be deemed to have
been sold when billed or shipped, whichever shall first occur, by such Affiliate
and said sale shall bear the  royalty.  In the case of a sale of  products  by a
sublicensee,  unless otherwise stated herein,  such sale shall bear the royalty.
Only one  royalty  shall be  payable  respecting  any  given  sale or use of any
specific  product licensed  hereunder.  

      4.7.  ImClone  hereby  covenants  and  agrees  that  it will  perform  all
calculations  with respect to the [ *** ] in good faith and in  accordance  with
generally accepted accounting principles in the United States.

      4.8.   Notwithstanding  any  other  provision  of  this  Article  IV,  the
obligation of Merck to pay royalties  under this Agreement  shall terminate upon
the  expiration of the term of the license,  as set forth in Section 2.5 hereof;
provided,  however, that nothing hereunder shall relieve Merck of its obligation
to pay any  royalties  under  this  Agreement  which have  accrued  prior to the
termination of this Agreement.

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      4.9. Manufacturing Facility.

            (a) Promptly  after the execution of this  Agreement,  ImClone shall
      use its  best  reasonable  efforts  to take  the  lead in  developing,  in
      consultation with Merck, a commercially  feasible production concept for a
      new manufacturing  facility of ImClone.  Such production  concept shall be
      proposed to Merck as soon as practicable, but in no event later than sixty
      (60) days after the date of this Agreement.  Upon ImClone's  proposal of a
      production concept to Merck, both parties shall negotiate in good faith to
      reach agreement on a commercially  feasible production concept;  provided,
      however,  that  Merck  shall have the right,  at its sole  discretion,  to
      reject a production concept.

            (b) Subject to the  parties'  reaching  agreement as to a production
      concept,  as described in Section 4.9(a) and Schedule 4.9, Merck agrees to
      provide to ImClone as soon as reasonably practicable after such agreement,
      a guarantee of a line of credit,  or a direct  credit,  for the purpose of
      funding  the new  manufacturing  facility of ImClone  (the  "Manufacturing
      Facility Line of Credit"),  which guarantee or direct credit,  as the case
      may be, shall  incorporate,  among other mutually agreed terms,  the terms
      set forth in Schedule 4.9. The manufacturing facility shall be constructed
      in accordance with the mutually agreed production concept, as described in
      Section 4.9(a) and Schedule 4.9. 

            (c) In the event that the  parties  fail to agree on a  commercially
      feasible production concept for the manufacturing  facility or Merck fails
      to provide the Manufacturing  Line of Credit within three months after the
      date of this Agreement,  either party,  provided that such party has fully
      performed  all of its  obligations  under Section  4.9(a),  shall have the
      right to terminate this Agreement upon notice to the other party, in which
      case  Merck  shall  have  no  further  obligations  with  respect  to  the
      Manufacturing  Facility  Line of  Credit.  

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            (d) Notwithstanding  any other provision of this Agreement,  if this
      Agreement  is  terminated  by either  party  pursuant  to Section  4.9(c),
      ImClone shall promptly repay Merck all Milestone Payments paid by Merck as
      of the date of such termination.

      4.10.  Royalties for the sale of Licensed Products,  Alternative  Products
and Merck  Products,  as the case may be,  arising out of sales in a  particular
country  shall be paid as  provided  in this  Agreement  but only to the fullest
extent permitted by law.

                                   ARTICLE V

                                Books and Records

      5.1.  Merck shall keep full and true books of account and other records in
sufficient  detail so that the  payments  to ImClone  hereunder  can be properly
calculated and audited.

      5.2. Each party agrees,  at the request and expense of the other party, to
permit an independent  certified public accountant selected by such other party,
barring a reasonable objection,  to have access at a single location,  once each
calendar year,  during ordinary business hours, to such books and records as may
be necessary, including any quantitative unit data that may be necessary for the
proper performance of the audit:

            (i) to  determine,  in respect to any calendar  year ending not more
      than five (5) years prior to the date of such request,  the correctness of
      any report and/or payment made under this Agreement; or

            (ii) to obtain  information  as to  royalties  payable  for any such
      period in case of failure to report  and/or pay  pursuant  to the terms of
      this Agreement.

                                   ARTICLE VI

                                 Confidentiality

      6.1.  ImClone shall  disclose to Merck and Merck shall disclose to ImClone
such  technology  as shall be  necessary  or  useful to assist  the  parties  in
successfully carrying out the objectives of this 

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Agreement, including, but not limited to, know-how and trade secrets, results of
the  Research and  Development,  Licensed  Product  Technology  and  Alternative
Product Technology (hereinafter "Confidential  Information").  Merck or ImClone,
as the case may be,  shall not,  during the term of this  Agreement  and for the
longer of the following:  (i) such time as there continue to be  royalty-bearing
sales  pursuant  to the  terms of  Section  2.5,  (ii) the life of all  Licensed
Product Patents and/or Alternative Product Patents, and (iii) ten years from the
execution  date of this  Agreement,  disclose  to any third  party  the  other's
Confidential  Information,  without the express written permission of the other;
shall  exercise the same degree of care as is exercised  with respect to its own
Confidential  Information to prevent  disclosure of the same to any third party;
and shall not use the same for any purpose  other than  exercising  any right or
rights granted to it herein;  provided,  however,  that nothing herein contained
shall  restrict  either  party  with  respect  to the  disclosure  and/or use of
information which the recipient party can show by written records:

            (i) was in its  possession  at the time of its  receipt of same from
      the disclosing party;

            (ii) was part of the public  knowledge or  literature at the time of
      its receipt from the disclosing  party, or thereafter  becomes part of the
      public  knowledge  or  literature  other  than  as a  result  of an act or
      omission to act on the part of the recipient; or

            (iii) was  received  from a third party having the right to disclose
      such information.

      Specific  technology  disclosed by one party to the other  hereunder shall
not be deemed to be within any of the above three (3) exclusions  merely because
it is  included  within  more  general  information  falling  within  one of the
exclusions.

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      6.2.  Notwithstanding  the  provisions  of Section  6.1 above,  and to the
extent necessary:

            (a) a party  may  disclose  and use the other  party's  Confidential
      Information  for  purposes  of  securing  the   registration  of,  and  or
      governmental  approval to market pursuant to this Agreement,  any Licensed
      Products or Alternative Products;

            (b) a party  may  disclose  and use the other  party's  Confidential
      Information  where  the  disclosure  and use of such  will  be  useful  or
      necessary  to the  procurement  of  patent  protection,  pursuant  to this
      Agreement,  for any  Improvement  relative  to any  Licensed  Products  or
      improvements relative to any Alternative Products; and

            (c) a party  may  disclose  and use the other  party's  Confidential
      Information  to the extent  that it is  necessary  or useful to aid in the
      development  and  commercialization,  pursuant to this  Agreement,  of any
      Licensed Products or any Alternative Products. 

                                  ARTICLE VII

                     Patent Filing, Maintenance and Expenses

      7.1.  With  respect to the filing of patent  applications  relating to the
Compound  or any  Improvement  exclusively  developed  or  acquired  by ImClone,
ImClone  shall be the  primary  filing  party in the  Territory  and outside the
Territory.  With  respect to the filing of patent  applications  relating to the
Compound or any Improvement that are exclusively  developed or acquired by Merck
or any of its Affiliates, Merck shall prepare and file a patent application in a
patent  office of its  choosing,  and shall be the primary  filing  party in the
Territory and outside the  Territory.  The primary  filing party shall cause the
applications  to be filed  through  its  attorneys.  All  expenses of the patent
applications  and/or patent filings,  prosecution and/or maintenance costs shall
be borne by the party that has the right to exploit the patent in the country in
which the application is filed.

      7.2.  In the case of patent  applications  relating to  compounds  jointly
developed  or acquired by the parties,  Merck shall be the primary  filing party
for filings in the Territory  and ImClone shall be the

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primary filing party for all filings  outside the Territory and each party shall
inform the other of all  activities  with  respect to filings,  prosecution  and
maintenance  of the patent  applications,  and shall  provide to the other party
copies  of  all  office   actions/official   actions  and  other  communications
concerning  said  applications  within  two (2)  weeks  after  receipt  thereof;
provided,  however,  that all applications shall first be filed  internationally
under the  Patent  Cooperation  Treaty  and  diligently  prosecuted  by a patent
attorney or patent agent mutually acceptable to the parties.  Both parties shall
be   apprised  by  such   patent   attorney  or  patent   agent  of  all  office
actions/official  actions  and shall be  entitled  for a period  of thirty  (30)
calendar  days, or such shorter  period of time as may be necessary in order not
to prejudice the parties'  rights  pursuant to such filings,  to review and make
comments  with  respect to all  applications  to and other  communications  with
patent authorities prior to the delivery or communication thereof.

      7.3.  Either party,  at its option and at its sole  expense,  may elect to
have the  normal  term of any  Licensed  Patent or  Alternative  Product  Patent
extended or restored  under a given  country's  procedure of extending  life for
time lost in government  regulatory  approval  processes.  The non-filing  party
shall assist the filing party and take whatever  reasonable  action is necessary
to obtain such extension. 

                                  ARTICLE VIII

                                  Infringement

      8.1. Each party to this Agreement  shall promptly  notify the other of any
material infringement of Licensed Product Patents or Alternative Product Patents
or  misappropriation  of Licensed  Product  Technology  or  Alternative  Product
Technology of which it becomes aware within the Territory, and shall provide the
other with any available evidence thereof. ImClone shall have the right, but not
the obligation,  to bring,  defend and maintain any appropriate  suit, action or
proceeding involving any such infringement (an "Infringement  Action").  ImClone
shall give Merck  notice of its  intention  to  commence  any such  Infringement
Action  and  Merck may at any time  elect to  participate  in such  Infringement
Action in accordance with Section 8.2.

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      8.2. In an Infringement  Action brought in accordance with Section 8.1(a),
Merck shall, upon the reasonable  request of ImClone,  cooperate with and assist
ImClone by, for example,  executing all papers and performing such other acts as
reasonably may be required and, at its option,  may be represented by counsel of
its choice at Merck's  expense.  Should ImClone lack standing or jurisdiction to
bring any  Infringement  Action,  Merck  shall do so at  ImClone's  request,  at
ImClone's expense.

      8.3.  Subject  to the right of Merck to be  represented  by counsel of its
choice,  ImClone  shall have the  exclusive  right to control  any  Infringement
Action brought,  defended or maintained by ImClone  pursuant to this Section 8.3
or by Merck  pursuant to the last  sentence of Section 8.2;  provided,  however,
that ImClone may not,  without the prior written consent of Merck (which consent
may not be unreasonably withheld), enter into any agreement or other arrangement
effecting a settlement of such Infringement Action.

      8.4. Subject to Section 8.5 hereof, any damages collected pursuant to this
Article  VIII  (whether  by judgment  or  settlement)  first shall be applied to
reimburse the parties for their respective  litigation expenses.  If the damages
are  insufficient  to reimburse both parties for such litigation  expenses,  the
parties shall receive  reimbursement  pro rata. Any remaining amounts of damages
shall be justly  and  equitably  distributed  between  the  parties  in order to
reflect the relative  benefits,  as reflected in the  royalties  provisions  set
forth in Section 4.2 hereof,  the parties would have received  hereunder but for
the  infringement or  misappropriation  that was the subject of the Infringement
Action.

      8.5.  If Merck  shall have  given  notice of a  material  infringement  of
Licensed  Product  Patents or  Alternative  Product  Patents in accordance  with
Section 8.1, and ImClone shall have failed to bring such an Infringement  Action
within  thirty (30) calendar days of receiving  such notice,  Merck,  at Merck's
expense,  shall have the right to bring and  maintain  an  Infringement  Action;
provided,  however,  that Merck may not,  without the prior  written  consent of
ImClone,  which  consent  shall not be  unreasonably  withheld,  enter  into any
agreement  or other  arrangement  effecting a  settlement  of such  Infringement

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Action.  Notwithstanding  any other  provision  in this  Agreement,  any damages
collected pursuant to this Section 8.5 (whether by judgment or settlement) shall
be paid in their entirety  solely to Merck.  

      8.6. If either party  institutes an Infringement  Action,  the other party
shall  fully  cooperate  with  and  supply  at its own  expense  all  assistance
reasonably  requested by the party which  instituted such  Infringement  Action.

                                   ARTICLE IX

                Representations and Warranties; Certain Covenants

      9.1. Representations and Warranties of ImClone.

      ImClone hereby represents and warrants that:

            (a) ImClone is a corporation duly incorporated, validly existing and
      in good  standing  under  the laws of the State of  Delaware,  and has all
      corporate powers and all governmental licenses, authorizations,  consents,
      permits,  registrations and approvals required to carry on its business as
      now  conducted  except  for such  matters  as would not have a  materially
      adverse effect on the business, assets or results of operations of ImClone
      and its  subsidiaries,  taken  as a whole,  and  except  any  such  effect
      resulting  from or arising in  connection  with (i) changes or  conditions
      affecting  the  biopharmaceuticals  industry  generally or (ii) changes in
      economic, regulatory or political conditions generally.

            (b) The  execution,  delivery  and  performance  by  ImClone of this
      Agreement  are  within  ImClone's  corporate  powers  and have  been  duly
      authorized by all necessary corporate action on the part of ImClone.  This
      Agreement   constitutes   a  valid  and  binding   agreement  of  ImClone,
      enforceable  in  accordance  with its terms,  subject  to (i)  bankruptcy,
      insolvency or similar laws affecting  creditors'  rights  generally,  (ii)
      general equitable principles and (iii) the Exon-Florio Act, Section 721 of
      Title VII of the Defense 

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      Production  Act of  1950,  as  amended,  and  the  rules  and  regulations
      promulgated thereunder.

            (c) Any Acquired Voting Shares or Milestone  Conversion  Shares,  at
      the time  issued  and  delivered  to Merck  pursuant  to  Section  4.1 and
      Schedule  E of this  Agreement,  shall be newly  issued  shares  of Common
      Stock, validly issued, fully paid and non-assessable and free and clear of
      any and all liens, encumbrances and claims of ownership of any kind of any
      third party and such Acquired Voting Shares or Milestone Conversion Shares
      shall be free of preemptive  or similar  rights.  Any Acquired  Non-Voting
      Shares,  at the time issued and delivered to Merck pursuant to Section 4.1
      and  Schedule  E of this  Agreement,  shall  be  newly  issued  shares  of
      non-voting  capital  stock of  ImClone,  validly  issued,  fully  paid and
      non-assessable  and free and clear of any and all liens,  encumbrances and
      claims  of  ownership  of any kind of any third  party  and such  Acquired
      Non-Voting  Shares shall be free of  preemptive or similar  rights.  Based
      only on the  market  price  of the  Common  Stock  as of the  date of this
      Agreement,  ImClone  represents  and warrants that a sufficient  number of
      shares of Common  Stock  has been  authorized  and  reserved  for  Merck's
      acquisition  of Acquired  Voting Shares and Milestone  Conversion  Shares.
      ImClone  covenants and agrees that a sufficient number of shares of Common
      Stock shall continue to be authorized and reserved for Merck' purchases of
      Acquired Voting Shares and Milestone Conversion Shares hereunder.


            (d) The  execution,  delivery  and  performance  by  ImClone of this
      Agreement  require no action by or in  respect  of, or  declaration  to or
      filing with, any governmental  body,  agency,  official or authority other
      than  compliance  with (i) any applicable  requirements  of the Securities
      Exchange Act of 1934, as amended (the "1934 Act") and state  securities or
      "blue sky" laws,  (ii) any applicable  requirements of Delaware law, (iii)
      the  rules and  regulations  of the  National  Association  of  Securities
      Dealers and the Nasdaq Stock 

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      Market,  and (iv) any  applicable  requirements  of the  Hart-Scott-Rodino
      Antitrust  Improvements  Act of  1976,  as  amended,  and  the  rules  and
      regulations promulgated thereunder (the "HSR Act").

            (e) The  execution,  delivery  and  performance  by  ImClone of this
      Agreement  do not and  will  not  (i)  contravene  or  conflict  with  the
      certificate  of  incorporation  or bylaws of ImClone;  (ii)  contravene or
      conflict  with or  constitute  a violation  of any  provision  of any law,
      regulation,   judgment,  injunction,  order  or  decree  binding  upon  or
      applicable  to ImClone;  (iii)  contravene,  conflict  with,  constitute a
      breach of or  default  under,  or give  rise to any right of  termination,
      cancellation  or acceleration of any right or obligation of ImClone under,
      any provision of any agreement,  contract or other instrument binding upon
      ImClone  or any of its  properties  or  (iv)  result  in the  creation  or
      imposition of any lien,  encumbrance  of claim of ownership of any kind by
      any third party on any asset, whether tangible or intangible, of ImClone.

            (f) ImClone  owns the Licensed  Product  Patents and such rights are
      not subject to any lien,  encumbrance or claim of ownership of any kind by
      any third party.

            (g) To ImClone's  knowledge the Licensed  Product  Patents are valid
      and enforceable.

            (h) To ImClone's knowledge,  ImClone has not engaged in any conduct,
      or  omitted to  perform  any  necessary  act,  the  result of which  could
      invalidate  any of the Licensed  Product  Patents or materially  adversely
      affect the enforceability of any of the Licensed Product Patents.

            (i) With the exception of the patents for which  Collateral  License
      Agreements  are to be obtained,  ImClone is unaware of any patent or claim
      by any third  party  upon the  basis of which  ImClone  has any  reason to
      believe that  Merck's  practice of the Licensed  Product  Technology  will
      infringe any valid patent. 

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<PAGE>

      9.2. Representations and Warranties of Merck.

      Merck hereby represents and warrants that:

            (a) Merck is a corporation with general partners duly  incorporated,
      validly  existing  and in good  standing  under  the  laws of the  Federal
      Republic of Germany,  and has all  corporate  powers and all  governmental
      licenses,  authorizations,  consents, permits, registrations and approvals
      required to carry on its business as now conducted except for such matters
      as would not have a materially  adverse effect on the business,  assets or
      results of operations of Merck and its subsidiaries, taken as a whole, and
      except any such effect  resulting  from or arising in connection  with (i)
      changes or conditions affecting the biopharmaceuticals  industry generally
      or (ii) changes in economic, regulatory or political conditions generally.

            (b)  The  execution,  delivery  and  performance  by  Merck  of this
      Agreement  are  within  Merck's   corporate  powers  and  have  been  duly
      authorized by all necessary  corporate  action on the part of Merck.  This
      Agreement constitutes a valid and binding agreement of Merck,  enforceable
      in accordance  with its terms,  subject to (i)  bankruptcy,  insolvency or
      similar laws affecting creditors' rights generally, (ii) general equitable
      principles and (iii) the Exon-Florio  Act, Section 721 of Title VII of the
      Defense Production Act of 1950, as amended,  and the rules and regulations
      promulgated thereunder.

            (c)  The  execution,  delivery  and  performance  by  Merck  of this
      Agreement  require no action by or in  respect  of, or  declaration  to or
      filing with, any governmental  body,  agency,  official or authority other
      than compliance with any applicable requirements of the HSR Act.

            (d)  The  execution,  delivery  and  performance  by  Merck  of this
      Agreement do not and will not (i)  contravene or conflict with the Satzung
      and other  constitutive  documents of

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      Merck;  (ii)  contravene or conflict with or constitute a violation of any
      provision of any law, regulation,  judgment,  injunction,  order or decree
      binding upon or applicable to Merck; or (iii)  contravene,  conflict with,
      constitute  a breach  of or  default  under,  or give rise to any right of
      termination,  cancellation  or  acceleration of any right or obligation of
      Merck under, any provision of any agreement,  contract or other instrument
      binding upon Merck or any of its properties.

            (e) In entering into this Agreement,  Merck has relied solely on its
      own scientific,  marketing and  distribution  expertise and experience and
      its analysis and evaluation of both the scientific and commercial value of
      the intended Licensed Products.

            (f) Merck  will  purchase  any  Acquired  Voting  Shares for its own
      account for investment only and not with a view towards the public sale or
      distribution  thereof except pursuant to sales  registered  under the U.S.
      Securities  Act of 1933,  as  amended  (the  "1933  Act") or an  exemption
      therefrom.

            (g) Merck is an  "accredited  investor"  as that term is  defined in
      Rule 501(a)(3) of Regulation D under the 1933 Act.

            (h) Merck  understands  that any Acquired  Voting  Shares,  Acquired
      Non-Voting Shares and Milestone Conversion Shares will be offered and sold
      to  it  in  reliance  on  specific   exemptions   from  the   registration
      requirements  of United States federal and state  securities laws and that
      ImClone will rely upon the truth and  accuracy of, and Merck's  compliance
      with, the  representations,  warranties,  agreements,  acknowledgments and
      understandings  of  ImClone  set forth  herein in order to  determine  the
      availability of such exemption and the eligibility of Merck to acquire any
      Acquired Voting Shares, Acquired Non-Voting Shares or Milestone Conversion
      Shares.

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            (i) Merck  and its  advisors,  if any,  will be  furnished  with all
      materials relating to the business, finances and operations of ImClone and
      materials  relating to the offer and sale of any Acquired  Voting  Shares,
      Acquired  Non-Voting  Shares or Milestone  Conversion  Shares requested by
      Merck. Merck and its advisors, if any, will be afforded the opportunity to
      ask questions of ImClone and receive complete and satisfactory  answers to
      any such inquiries.  Merck understands that its investment in any Acquired
      Voting Shares,  Acquired Non-Voting Shares or Milestone  Conversion Shares
      will involve a high degree of risk.

            (j) Merck  understands that no United States federal or state agency
      or any other  government or  governmental  agency will pass on or make any
      recommendation  or  endorsement of any Acquired  Voting  Shares,  Acquired
      Non-Voting Shares or Milestone Conversion Shares.

            (k) Merck  understands  that the Acquired  Voting  Shares,  Acquired
      Non-Voting  Shares and Milestone  Conversion Shares have not been, are not
      being,  and will not be registered under the 1933 Act or any United States
      state securities laws or any other laws, and may not be transferred unless
      subsequently  registered  thereunder or pursuant to an exemption from such
      registration  and, except as specified in this agreement,  neither ImClone
      nor any other Person is under any  obligation to register such  securities
      under the 1933 Act or any  state  securities  laws or to  comply  with the
      terms and conditions of any exemption thereunder.

            (l) Merck agrees (and shall cause each of its  Affiliates  to agree)
      that in no event shall it make a disposition,  directly or indirectly,  of
      such Acquired  Non-Voting Shares other than to Merck or to an Affiliate of
      Merck,  unless it shall have first  obtained the prior written  consent of
      ImClone.  

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            (m) Merck  understands  that any Acquired  Voting  Shares,  Acquired
      Non-Voting  Shares and Milestone  Conversion Shares may bear a restrictive
      legend in substantially the following form (and a stop-transfer  order may
      be placed against transfer of such stock certificates):

                  THE SECURITIES  REPRESENTED BY THIS  CERTIFICATE HAVE NOT BEEN
                  REGISTERED UNDER THE UNITED STATES  SECURITIES ACT OF 1933, AS
                  AMENDED.  THE SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT AND
                  MAY NOT BE SOLD,  TRANSFERRED OR ASSIGNED  UNLESS AN EFFECTIVE
                  REGISTRATION  STATEMENT FOR THE  SECURITIES  UNDER SAID ACT OR
                  PURSUANT TO AN EXEMPTION FROM SUCH REGISTRATION.

      9.3. The parties hereby covenant and agree as follows:

                  (a) ImClone  covenants that at no time during the term of this
            Agreement or at any time thereafter,  so long as Merck shall enjoy a
            right  originating  under  this  Agreement,  shall  ImClone  assign,
            transfer,  encumber,  hypothecate or grant rights in or with respect
            to any Licensed  Product and/or  Alternative  Product to any Person,
            including any Affiliate of ImClone, inconsistent with the grants and
            other rights reserved to Merck under this Agreement.

                  (b) Merck  covenants  that at no time  during the term of this
            Agreement or at any time thereafter,  so long as ImClone shall enjoy
            a  right  originating  under  this  Agreement  shall  Merck  assign,
            transfer,  encumber,  hypothecate or grant rights in or with respect
            to any Licensed  Product and/or  Alternative  Product to any Person,
            including any Affiliate of Merck,  inconsistent  with the grants and
            other rights reserved to ImClone under this Agreement.


      9.4.  ImClone hereby  covenants and agrees that it shall not, for a period
of six months after the execution of this  Agreement,  without the prior written
consent of Merck,  directly or indirectly,  take (nor

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shall  ImClone   authorize  or  permit  its  officers,   directors,   employees,
representatives,  investment bankers, attorneys,  accountants or any other agent
or any Affiliate of ImClone, to take) any action to:

            (a) encourage, solicit or initiate the submission of any Acquisition
      Proposal (as defined below);

            (b) except as permitted below, enter into any agreement with respect
      to or propose any Acquisition Proposal; or

            (c) except as permitted below, participate in any way in discussions
      or  negotiations  with, or furnish any  information  to, any Person (other
      than  Merck,  its  Affiliates  or  its  officers,  directors,   employees,
      representatives,  investment  bankers,  attorneys,  accountants  or  other
      agents  of  Merck)  in  connection  with,  or take  any  other  action  to
      facilitate  any inquiries or the making of any proposal that  constitutes,
      or may reasonably be expected to lead to, any Acquisition Proposal;

      provided,   however,  that  ImClone  may  participate  in  discussions  or
negotiations or enter into an agreement  (including as a part thereof making any
counter-proposal)  with or furnish information to any third party (so long as it
has complied with this Section 9.4) if the Board of Directors determines in good
faith,  based upon advice of outside  counsel,  that the failure to provide such
information  or participate in such  discussions or  negotiations  or consummate
such  Acquisition  Proposal  would  cause  the  directors  to  be  subject  to a
substantial  risk of breach of their  fiduciary  duties under  Delaware law. For
purposes  of this  Agreement,  "Acquisition  Proposal"  shall mean any bona fide
proposal made to acquire (i)  beneficial  ownership (as defined under Rule 13d-3
under the 1934 Act) of a 10% or greater equity interest in ImClone in any single
or multi-step  transaction or series of related transactions which is structured
to permit any Person to acquire beneficial  ownership of a 10% or greater equity
interest  in  ImClone  or (ii) a  material  part of the  business  or  assets of
ImClone.  ImClone hereby  acknowledges and agrees that Merck

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has  agreed to enter  into this  Agreement  in  reliance  on the  covenants  and
agreements set forth in this Section 9.4.

      9.5. As a condition to Merck's entering into this Agreement and making the
Milestone  Payments,  Merck  shall  receive,  respectively,  on the  date of the
execution of this  Agreement and on the date of the issuance of Acquired  Voting
Shares,  Acquired  Non-Voting  Shares or Milestone  Conversion  Shares to Merck,
opinion  letters  of the  general  counsel  of  ImClone,  in form and  substance
satisfactory  to  Merck,  substantially  in the form set  forth in  Schedule  H,
attached hereto and specifically incorporated herein.

      9.6.  Subject to Section 11.7 hereof,  ImClone hereby covenants and agrees
to use its best  reasonable  commercial  efforts to negotiate and enter into, at
the earliest  practicable date, all of the Collateral License Agreements,  which
agreements  shall be in form and  substance  reasonably  satisfactory  to Merck.
Merck hereby covenants and agrees to use its best reasonable  commercial efforts
to cooperate  with ImClone to take any  appropriate  action  and/or  execute any
documents of any kind which may be  reasonably  necessary for ImClone to fulfill
its  obligations  under this Section 9.6. Each party shall bear its own expenses
with respect to the  negotiation  of such  agreements.  Merck and ImClone  shall
share  equally  the  payment  of  royalties  due  under the  Collateral  License
Agreements in the Territory ("Collateral License Agreement Royalties").

      9.7.  Merck  hereby  covenants  and  agrees  that all  sales  of  Licensed
Products,  Alternative  Products and Merck Products  pursuant to this Agreement,
other than sales to Merck's Affiliates, shall be made on an arms-length basis.

      9.8.  Merck shall use its best  reasonable  commercial  efforts to develop
(including the timely and diligent pursuit of clinical trials and all applicable
regulatory  approvals)  and market the Licensed  Products  within the Territory;
provided,  however, that Merck shall have the right, at its sole discretion, 

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not to develop and market the Licensed  Products in a given  country in order to
optimize sales of Licensed Products within the Territory taken as a whole. 

      9.9. Standstill.

            (a) During the  Standstill  Period  Merck  shall not,  and shall not
      permit its Affiliates to, purchase or otherwise  acquire  (whether through
      conversion of the Series A Convertible  Preferred  Stock,  acquisition  of
      Acquired  Voting  Shares  or  Acquired  Non-Voting  Shares  or  conversion
      thereof,  open-market purchases,  privately-negotiated  purchases, merger,
      tender  offer or  otherwise),  or agree or offer to purchase or  otherwise
      acquire (whether through conversion of the Series A Convertible  Preferred
      Stock,  acquisition  of  Acquired  Voting  Shares or  Acquired  Non-Voting
      Shares,  open-market purchases,  privately-negotiated  purchases,  merger,
      tender offer or otherwise)  beneficial ownership of any Voting Securities,
      if after giving effect thereto Merck and its Affiliates would beneficially
      own Voting Securities  representing more than 19.9% of Total Voting Power.
      As used herein,  "Total Voting Power" means the aggregate  number of votes
      which may be cast by holders of outstanding  Voting Securities and "Voting
      Securities"  means all  securities  of ImClone  entitled,  in the ordinary
      course,  to vote in the election of directors of ImClone.  As used in this
      Agreement,  the terms "beneficial  ownership" and "beneficially own" shall
      be determined in accordance with Rules 13d-3 and 13d-5 under the 1934 Act;
      provided,  however,  that for purposes of this Section 9.9(a) only,  Merck
      shall not be deemed to  beneficially  own any  Common  Stock  which may be
      issued solely upon  conversion of the Series A Preferred  Stock until such
      time as such  Series A Preferred  Stock is  converted  into Common  Stock;
      provided,   further,  that  nothing  herein  shall  permit  Merck  or  its
      Affiliates  during the Standstill Period to convert any Series A Preferred
      Stock if after such conversion Merck and its Affiliates would beneficially
      own Voting Securities  representing more than 19.9% of Total Voting Power.
      Notwithstanding  

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      anything in this Agreement to the contrary, beginning on the date which is
      six months from the date of the  execution  of this  Agreement  and ending
      upon the  conclusion of the  Standstill  Period,  Merck and its Affiliates
      shall not directly or indirectly  purchase or otherwise acquire beneficial
      ownership of Voting Securities through open-market or privately-negotiated
      transactions.

(b) During  the  Standstill  Period  Merck  shall not,  and shall not permit its
Affiliates to (i) make, or take any action to solicit, initiate or encourage, an
Acquisition  Proposal;   (ii)  "solicit,"  or  become  a  "participant"  in  any
"solicitation"  of, any  "proxy" (as such terms are  defined in  Regulation  14A
under the 1934 Act) from any holder of Voting  Securities in connection with any
vote on any matter,  or agree or announce its  intention to vote with any Person
undertaking a  "solicitation";  (iii) form,  join or in any way participate in a
"group" (within the meaning of Section 13(d)(3) of the 1934 Act) with respect to
any  Voting  Securities;  (iv)  grant any  proxies  with  respect  to any Voting
Securities to any Person (other than as recommended by the Board of Directors of
ImClone) or deposit any Voting  Securities  in a voting  trust or enter into any
other  arrangement  or  agreement  with  respect to the voting  thereof;  or (v)
assist,  advise or  encourage  any Person with respect to, or seek to do, any of
the foregoing.  

            (c) Merck  agrees  that any breach by it of this  Section  9.9 would
      irreparably  injure  ImClone and that money damages would be an inadequate
      remedy therefor.  Accordingly, Merck agrees that ImClone shall be entitled
      to one or  more  injunctions  enjoining  any  such  breach  and  requiring
      specific  performance  of this  Section  9.9  and  consents  to the  entry
      thereof,  in addition to any other remedy to which  ImClone is entitled at
      law or in equity.

            (d) This Section 9.9 shall  supercede  Section 4(e) of the Preferred
      Stock  Purchase  Agreement,  which  Section  4(e)  shall be of no  further
      effect.

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      9.10. Prohibited Transactions.  Merck hereby agrees that it shall not (and
shall not permit any Affiliate or any sublicensee or its Affiliate to), directly
or indirectly,  sell,  export,  reexport,  transmit or transfer (i) any Licensed
Products,  Alternative  Products,  Licensed  Product  Technology or  Alternative
Product   Technology  or  (ii)  any  products,   technology  or  technical  data
incorporating  any of the  foregoing  to (a) any  countries  or Persons that are
subject to restrictions under the U.S. Export  Administration  Regulations;  (b)
any end-user  which Merck knows or has reason to know will utilize such Licensed
Products,  Alternative  Products or Licensed  Product  Technology in the design,
development or production of nuclear, chemical or biological weapons; or (c) any
other country or Person to which the sale,  export,  reexport,  transmission  or
transfer is restricted pursuant to U.S. economic sanctions laws and regulations,
including but not limited to the  restrictions  set forth at Title 31, Chapter V
of the Code of Federal  Regulations;  in each case of clauses  (a),  (b) and (c)
above without the prior written  consent of the Bureau of Export  Administration
of the U.S. Department of Commerce,  the Office of Foreign Assets Control of the
U.S.  Department of the Treasury,  and/or such other governmental  entity as may
have jurisdiction over such sale, export,  reexport,  transmission,  transfer or
transactions. Merck hereby covenants and agrees that it shall not (and shall not
permit any Affiliate or any  sublicensee or its Affiliate to) require ImClone or
any of its  Affiliates  to take any of the actions  proscribed  pursuant to this
Section 9.10.

      9.11.  Merck hereby  covenants and agrees that it shall not (and shall not
permit any Affiliate or any sublicensee or its Affiliate) directly or indirectly
to sell or otherwise transfer any Licensed Products or Alternative  Products (i)
outside the Territory or (ii) to any Person which Merck or any of its Affiliates
or any  sublicensee or its Affiliate knows or has reason to know intends to use,
sell or transfer Licensed Products or Alternative Products in or to any location
outside of the Territory.

      9.12. ImClone hereby covenants and agrees that it shall not (and shall not
permit any Affiliate or any sublicensee or its Affiliate) directly or indirectly
to sell or otherwise transfer any Licensed Products or Alternative  Products (i)
within  the  Territory  or  (ii)  to  any  Person  which  ImClone  or any of its

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Affiliates  or any  sublicensee  or its  Affiliate  knows or has  reason to know
intends to use, sell or transfer Licensed Products or Alternative Products in or
to any location within of the Territory. 

                                   ARTICLE X

                                 Indemnification

      10.1.  ImClone  shall  indemnify,  hold  harmless and defend Merck and its
Affiliates  from and  against  any and all Losses  resulting  directly  from any
claims or actions for patent infringement, or from any judgment entered therein,
which  may  be  brought  against  Merck  or any of  its  Affiliates  for  patent
infringement  as a result of its  activities  under the  Agreement in connection
with the  development  or  commercialization  of the  Compound,  except  for (a)
potential claims or actions (other than potential claims or actions with respect
to the Collateral  License  Agreements and the related patent  applications  and
patents) of which Merck and its Affiliates have actual  knowledge as of the date
of this  Agreement and (b) potential  claims or actions based on patents not yet
issued unless, as of the date of this Agreement,  ImClone had or should have had
knowledge of such patents.

      10.2. Prior to the  commercialization of Licensed Products and Alternative
Products,  respectively,  in the  Territory,  each party shall  indemnify,  hold
harmless  and  defend  (the  "Indemnifying  Party")  the  other  party  and  its
Affiliates (each, an "Indemnified Party") against any and all Losses suffered by
an Indemnified  Party arising out of,  relating to, or based upon any claim by a
third party, or in any criminal or regulatory proceeding, relating or pertaining
in any way to a  Licensed  Product or  Alternative  Product,  including  but not
limited to claims that (a) a Licensed  Product or Alternative  Product was or is
unsafe,  unfit or otherwise  deficient in quality or condition or (b) a Licensed
Product or Alternative  Product caused any death or personal injury of any kind,
including but not limited to any death or personal injury  occurring  during the
conduct of any clinical  trial,  in each case,  to the extent that such Loss was
directly or  indirectly  caused by  services  performed  or actions  taken by an
Indemnifying Party or its employees, agents or subcontractors, including but not
limited to the manufacture,  design, packaging, shipment, handling or storage of
any  Licensed  Product  or  Alternative  Product,  as the case may 

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be. Upon the  commercialization  of any Licensed Product or Alternative Product,
as the case  may be,  the  parties  hereby  agree  that  the  respective  supply
agreements that are to be negotiated,  as described in Section 3.8 hereof, shall
include  usual and customary  terms of  indemnification  for similar  agreements
under comparable circumstances.

      10.3.  ImClone  shall  indemnify,  hold  harmless and defend Merck and its
Affiliates against any and all Losses suffered by Merck arising out of, relating
to, or based  upon 

            (a) the breach of any  representation or warranty made by ImClone in
      this Agreement, or

            (b) the breach or failure to perform by ImClone of any  agreement or
      covenant contained in this Agreement.

      10.4.  Merck shall  indemnify,  hold  harmless and defend  ImClone and its
Affiliates  against  any and all  Losses  suffered  by ImClone  arising  out of,
relating to, or based upon

            (a) the breach of any  representation  or warranty  made by Merck in
      this Agreement, or

            (b) the breach or failure  to perform by Merck of any  agreement  or
      covenant contained in this Agreement.

      10.5. This Article X shall survive the termination of the Agreement.

                                   ARTICLE XI

                            Duration and Termination

      11.1. This Agreement,  unless it is sooner  terminated as herein provided,
shall  remain in full force and effect for that  period or periods  set forth in
Section 2.5 hereof.

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<PAGE>

11.2.  The parties may mutually agree at any time to terminate this Agreement at
a fixed date. Prior to or at termination,  as the case may be, if any portion of
any royalty  payment  under  Article IV is due ImClone  through the  agreed-upon
      termination  date,  based on a proration  according to calendar time, such
portion
shall be paid by Merck to ImClone.  

      11.3.  On  each  Milestone  Payment  Date  after  the  execution  of  this
Agreement,  Merck shall have the unconditional right, at its sole discretion, to
terminate  this  Agreement  by  delivering  a written  notice to that  effect to
ImClone,  in which case Merck shall have no  obligation to make any payment with
respect to any Milestone  Payment that otherwise would have been due and payable
on such Milestone Payment Date but for the operation of this Section 11.3.

      11.4.  If,  within  one year of the  first  commercial  sale of the  first
Licensed Product in the Territory,  Merck  reasonably  determines that it is not
economically  feasible to market Licensed Products in the Territory,  then Merck
shall have the right, upon written notice delivered to ImClone, to terminate the
development  and sale of  Licensed  Products  in the  Territory,  in which  case
ImClone  shall be obligated to repay Merck 50% of all cash amounts paid by Merck
with  respect to Milestone  Payments as of such date;  provided,  however,  that
ImClone  shall not be  obligated  to repay  Milestone  Payments  in  respect  of
purchases  by Merck of  Acquired  Voting  Shares or Acquired  Non-Voting  Shares
pursuant to Section 4.1 and Schedule E hereof;  provided,  further, that ImClone
only shall be  required  to make such  repayments  out of  revenues  received by
ImClone  from the sale of Licensed  Products in the United  States and Canada at
the rate of [ *** ] of the [ *** ] of such sales in Canada and the United States
for the first [ *** ] and [***] of the [ *** ] of any such  sales in Canada  and
the United  States in excess of [ *** ];  provided,  further  that to the extent
ImClone  shall have  sublicensed  Licensed  Products  to a Person  other than an
Affiliate of ImClone,  ImClone  only shall be required to make such  payments at
the rate of [ *** ] of the fees and royalties  received from such sublicensee on
account of the sale of Licensed Products in the United States and Canada.  

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<PAGE>

      11.5.  In the event that Merck or ImClone shall at any time default in the
performance  of any of the material  covenants or conditions  contained  herein,
Merck or ImClone,  as the case may be,  shall have the right to notify the other
of such default and that the notifying party intends to terminate this Agreement
unless such default is corrected.  Unless such default shall be corrected by the
defaulting  party  within  sixty (60)  calendar  days from receipt by it of such
notice,  the  notifying  party  shall be  entitled,  by notice to the other,  to
terminate  this  Agreement at any time after the end of the sixty (60)  calendar
day period if the default continues.

      11.6. Either party may terminate this Agreement and the license hereunder,
by delivering a written  notice to that effect to the other party,  in the event
that such other party:

            (a) is the subject of an order for relief by a bankruptcy court;

            (b)  applies for or consents  to the  appointment  of any  receiver,
      trustee, custodian,  conservator,  liquidator,  rehabilitator,  or similar
      officer for it or for all or  substantially  all of its  property;  or any
      receiver, trustee, custodian, conservator,  liquidator,  rehabilitator, or
      similar  officer is appointed  without the  application or consent of such
      other party and the  appointment  continues  undischarged  or unstayed for
      sixty (60) calendar days; or

            (c)   institutes  or  consents  to  any   bankruptcy,   proposal  in
      bankruptcy, insolvency, reorganization, arrangement, readjustment of debt,
      dissolution, custodianship,  conservatorship, liquidation, rehabilitation,
      or similar proceeding relating to all or substantially all of its property
      under the laws of any jurisdiction.

      11.7.  ImClone  acknowledges  and agrees that the  execution of all of the
necessary   Collateral  License  Agreements  is  integral  to  the  transactions
contemplated  herein.  If, as of the first  anniversary of the date on which all
patents and patent applications referred to in the first paragraph of Schedule F
are deemed valid and no longer  subject to opposition  or appeal,  ImClone shall
not have (i) entered  into all of the  Collateral  License  Agreements,  or (ii)
demonstrated  to the  satisfaction  of Merck that some or all of 

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                                       40
<PAGE>

such  agreements  are either not necessary or are required to be entered into by
Merck   rather  than   ImClone  and  ImClone  has  entered  into  those  not  so
demonstrated,  then Merck shall have the right, at its sole option, upon written
notice delivered to ImClone, to terminate this Agreement,  in which case ImClone
shall be  obligated  to repay in full all cash amounts with respect to Milestone
Payments paid by Merck as of the date of such notice of  termination;  provided,
however, that Merck shall retain all its rights with respect to the Chemotherapy
Patent and Radiotherapy  Patent, as provided in Section 2.2 hereof,  and Section
2.2 and Section 4.2(d) shall survive termination of this Agreement.  The parties
acknowledge  and agree that the actual  amount of damages that would be suffered
by Merck if ImClone or Merck, as the case may be, fails to enter into all of the
Collateral  License  Agreements before the first  anniversary  referred to above
cannot be, or would be difficult to, determine. It is hereby agreed,  therefore,
that if  ImClone  or Merck,  as the case may be,  fails to enter into all of the
Collateral  License Agreements within said one-year period,  then ImClone,  upon
written  demand from Merck,  shall be  obligated to pay to Merck within ten (10)
calendar  days  of  ImClone's  receipt  of  such  written  demand,  $500,000  as
liquidated  damages.  This payment of liquidated damages shall be in addition to
the repayments of Milestone Payments described above in this Section 11.7 and to
any other  rights to  indemnification  or damages to which Merck may be entitled
hereunder or according to any applicable law.

      11.8.  Upon  termination of this  Agreement,  the license and other rights
granted herein shall terminate in accordance  with the  appropriate  provisions,
and all rights related to the terminated  portion of the license shall revert to
the party(ies) herein which are their respective original licensors.

      11.9.  Termination  or  expiration  of this  Agreement  shall  be  without
prejudice to the right of any party that is not in default  hereunder to receive
all payments  accrued and unpaid at the  effective  date of such  expiration  or
termination,  to the remedy of either party in respect to any previous breach of
any of the covenants herein contained,  and to any other provisions herein which
expressly  or  necessarily  call  for  performance   after  such  expiration  or
termination.  Article I,  Section  2.2,  Section 3.7,  Section  4.1(c),  Section
4.2(d), Section 4.3, Section 4.4, Section 4.5, Section 4.6, Section 4.8, Section
4.9(d),  Section 4.10

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                                       41
<PAGE>

(only  with  respect  to Merck  Products),  paragraphs  2 and 4 of  Schedule  E,
Schedule G, Article V, Article VI, Section  9.2(h),  (i), (j), (k), (l) and (m),
Section 9.7 (only with respect to Merck  Products),  Section 9.9,  Section 9.10,
Section 9.11, Article X, Section 11.8, Section 11.9, Article XIII, Section 16.2,
Section 16.4,  Section 16.5,  Section 16.6,  Section 16.7 and Section 16.8 shall
survive expiration or termination.

      11.10.  If Merck  fails in a country in which  Merck has the right to sell
Licensed Products or Alternative Products to pursue in a timely fashion and with
all  due  diligence  regulatory  approval  or  sale  of a  Licensed  Product  or
Alternative  Product, and such failure is not remedied within one hundred twenty
(120) calendar days after written notice from ImClone  specifying  such failure,
ImClone may  immediately,  upon written  notice to Merck,  terminate the license
with  respect to such  Licensed  Products  and/or  Alternative  Products in such
country;  provided,  however,  that  Merck  shall  have the  right,  at its sole
discretion,  not to pursue such regulatory approvals or sales in a given country
in order to optimize sales within the Territory  taken as a whole, in which case
ImClone shall not have the right to terminate  such license with respect to such
country pursuant to this Section 11.10. 

                                  ARTICLE XII

                             Successors and Assigns

      12.1. The provisions of this Agreement  shall be binding upon and inure to
the benefit of the parties hereto and their respective  successors and permitted
assigns.  Neither  party may assign,  delegate or otherwise  transfer any of its
rights or obligations  under this Agreement without the prior written consent of
the other party hereto  except to the successor of all or  substantially  all of
the assigning party's  pharmaceutical  business (whether by merger,  asset sale,
operation of law or otherwise).

      12.2. Notwithstanding the foregoing, Merck may assign its rights, in whole
or in part,  and  delegate  its  duties  and  obligations,  in whole or in part,
without  the  consent  of ImClone to a  directly  or  indirectly  majority-owned
subsidiary  of Merck,  (the  "Assignee")  which  Assignee  shall  enter  into an

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                                       42
<PAGE>

assignment and assumption agreement acceptable in form and substance to ImClone.
In the  event  that  Merck  assigns  its  rights or  delegates  its  duties  and
obligations  hereunder in  accordance  with this Article XII, all  references to
Merck  shall refer to the  Assignee  as well as to Merck and Merck shall  remain
primarily liable for the performance of its obligations hereunder.

                                  ARTICLE XIII

                                   Arbitration

      13.1.  Any dispute  between the parties,  relating to the  interpretation,
implementation  or  application  of this  Agreement  which cannot be resolved by
negotiation shall be settled by arbitration,  at the request of either party, by
written notice to the other,  under the  Commercial  Rules of Arbitration of the
American  Arbitration  Association  as in effect at the time  such  request  for
arbitration is made, except that each party shall select one arbitrator, and the
two arbitrators thus selected shall thereafter select a third in accordance with
the aforesaid  Rules of the American  Arbitration  Association.  The arbitration
shall be conducted at the  domicile of the  defendant.  All expenses and fees of
the arbitrators  shall be divided  equally between the parties unless  otherwise
ordered by the arbitrators.  The award in any such arbitration  proceeding shall
be final and  binding  upon the  parties  and shall not be  subject to appeal or
other legal recourse by either party.  This provision  shall not be construed to
preclude any action for an injunction or other equitable relief before any court
of competent jurisdiction.

                                  ARTICLE XIV

                                     Notices

      14.1. Any notice  expressly  provided for under this Agreement shall be in
writing, shall be given either manually, by express courier, or by facsimile and
shall be  deemed  sufficiently  given if and when  received  by the  party to be
notified as follows:

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                                       43
<PAGE>

if Merck, to:

Frankfurter Stra(beta)e 250

D-64293 Darmstadt

Federal Republic of Germany

Attention: Klaus-Peter Brandis

Facsimile:  011-49-6151-72-7773,

with a copy (which shall not constitute notice) to:

Rogers & Wells LLP

200 Park Avenue

New York, New York 10166 USA

Attention: Klaus H. Jander, Esq.

Facsimile:  (212) 878-8375; and


if to ImClone, to:

180 Varick Street

New York, New York, 10014 USA

Attention: John B. Landes, Esq.

Facsimile: (212) 645-2054

with a copy (which shall not constitute notice) to

Davis Polk & Wardwell

450 Lexington Avenue

New York, New York 10017 USA

Attention: Phillip R. Mills, Esq.

Facsimile: (212) 450-4800.

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                                       44
<PAGE>

                                   ARTICLE XV

                                Entire Agreement

      15.1. This Agreement  constitutes the entire  agreement  between Merck and
ImClone  relating to the subject matter hereof.  No variation or modification of
this Agreement,  or waiver of any of the terms or provisions  thereof,  shall be
deemed valid unless in writing as an amendment hereto, signed by both parties.

                                  ARTICLE XVI

                                  Miscellaneous

      16.1. The parties hereby represent and warrant that the persons  executing
this Agreement below hold the offices designated,  that they are duly authorized
to execute this Agreement and thereby bind the  respective  parties to its terms
and provisions, and that all required approvals of each signatory's superiors or
any committee or board have been obtained.

      16.2. This Agreement shall be governed by and construed in accordance with
the laws of the State of New York without regard to the  conflicts-of-law  rules
of such State.

      16.3. This Agreement may be signed in any number of counterparts,  each of
which shall be an original,  with the same effect as if the  signatures  thereto
were upon the same instrument.

      16.4. The captions  herein are included for  convenience of reference only
and shall be ignored in the construction or interpretation hereof.

      16.5.  After the  execution of this  Agreement,  the parties  hereto shall
cooperate  with one another to take any  appropriate  action and/or  execute any
documents  of any kind  which  may be  reasonably  necessary  to  carry  out any
provision of this  Agreement,  including but not limited to preparing and filing
any required  notifications under the HSR Act in connection with the issuance of
Acquired  Voting  Shares,  Acquired  Non-Voting  Shares or Milestone  Conversion
Shares to Merck.  

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                                       45
<PAGE>

      16.6. No failure or delay by either party in exercising  any right,  power
or privilege hereunder shall operate as a waiver thereof nor shall any single or
partial  exercise  thereof preclude any other or further exercise thereof or the
exercise of any other right, power or privilege.  The rights and remedies herein
provided  shall be  cumulative  and not  exclusive  of any  rights  or  remedies
provided by law.

      16.7. Force Majeure. Neither party shall be liable for delay or failure to
perform this Agreement,  in whole or in part, by reason of contingencies  beyond
the  reasonable  control  of the party  affected,  whether  herein  specifically
enumerated  or not,  including  among  others,  acts of God,  war,  acts of war,
revolution, civil commotion, riots, acts of public enemies, blockage or embargo,
delays of carriers,  car shortage,  fire,  explosion,  breakdown of equipment or
facilities,  strike, lockout, labor dispute,  casualty or accident,  earthquake,
epidemic,  flood,  cyclone,  tornado,  hurricane or other  windstorm,  delays of
vendors or other contingencies  interfering with production or with customary or
usual means of transportation of raw materials or products or with the supply of
coal,  natural gas, oil or fuel, or by reason of any law,  order,  proclamation,
regulation,  ordinance,  demand,  requisition or requirement or any other act of
any governmental authority, local, state, provincial or federal, including court
orders,   judgments  or  decrees,  or  actions  of  any  governmental  authority
respecting  the   registration,   re-registration,   cancellation,   suspension,
labeling,  and/or  ability to  transport  or sell  products,  or any other cause
whatsoever,  whether similar or dissimilar to those enumerated above;  provided,
that the party so  affected  shall  within 24 hours give  written  notice to the
other  party  whenever  such   contingency  or  other  act  becomes   reasonably
foreseeable  and shall use its best  efforts  to  overcome  the  effects  of the
contingency as promptly as possible.  Neither party shall be required to resolve
a strike,  lockout or other  labor  problem in a manner  which it alone does not
deem proper and advisable. The party affected by an event of the sort enumerated
in or contemplated by this Section may suspend performance of this Agreement for
a period of time equal to the duration of the event  excusing such  performance.

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<PAGE>

      16.8. Nothing contained herein shall, by virtue of this Agreement,  create
a partnership,  joint  venture,  agency or employment  relationship  between the
parties  hereto.  No agent or employee or either party hereto shall be the agent
or  employee of the other party by virtue of this  Agreement.  

      16.9.  Nothing in this Agreement  shall require ImClone to take any action
in connection with the issuance of any of its securities  that would  contravene
any federal or state securities laws applicable to ImClone.

      16.10. Any notices to third parties and all other publicity concerning the
existence and terms of this Agreement and the transactions  contemplated  hereby
shall be jointly planned and  coordinated by the parties  hereto.  Neither party
shall act  unilaterally  in this regard without the prior written consent of the
other party, which consent shall not be unreasonably  withheld.  Notwithstanding
the  foregoing  provisions  of this  Section  16.10,  either party may make such
announcements of, and/or provide publicity  concerning,  the existence and terms
of this  Agreement  and the  transactions  contemplated  hereby as is reasonably
necessary or advisable,  in the opinion of such party's counsel,  to comply with
the provisions of any applicable law or regulation, including but not limited to
filings  with  the  U.S.   Securities  and  Exchange  Commission  or  any  other
governmental  authority or with the National  Association of Securities Dealers;
provided,  however, that to the extent practical each party shall give the other
party prior notice of any such announcement or publicity.

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<PAGE>

      IN WITNESS  WHEREOF,  this  Agreement  has been executed on the date first
above written.

                                          IMCLONE SYSTEMS INCORPORATED

                                          By: /s/ Dr. Samuels D. Waksal
                                              ---------------------------------
                                          Name:  Dr. Samuel D. Waksal
                                          Title: President


                                          MERCK KGaA

                                          By: /s/Prof. Dr. Bernhard Scheuble
                                              --------------------------------- 
                                          Name:  Prof. Dr. Bernhard Scheuble
                                          Title: General Partner, member of the
                                                 Executive Board, and CEO Pharma

                                          By: /s/ Klaus Peter Brandis
                                              --------------------------------- 
                                          Name:  Klaus-Peter Brandis
                                          Title: Head of Legal Department

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<PAGE>

                                    SCHEDULES

                                  SCHEDULE 2.8

Proposed License Agreement between ImClone and [ *** ] concerning exclusive
licensing by ImClone of intellectual property rights of ImClone in up to [***].

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<PAGE>

                                  SCHEDULE 4.9
                 FINANCING ASSISTANCE FOR MANUFACTURING FACILITY
                                 PROPOSED TERMS

The  Manufacturing  Facility  Line of  Credit  shall  incorporate,  among  other
mutually agreed terms, the following terms:

Financing Assistance:         Financing  assistance  will be  provided  by Merck
                              either  in  the  form  of  (i) a  credit  facility
                              directly  to ImClone  ("Direct  Credit") or (ii) a
                              guaranty of payment to a commercial bank providing
                              such  credit  facility  to  ImClone  ("Guaranty");
                              provided,  however, that such financing assistance
                              shall be subject to the prior approval by Merck of
                              a production concept, and such assistance shall be
                              exclusively  for the  realization of that concept.
                              In  either  case,  the  credit  facility  shall be
                              accessed by ImClone  through the issuance of notes
                              (each, a "Note" and, collectively, the "Notes").

                              The   Steering    Committee   may   recommend   an
                              alternative  project to be  undertaken  to provide
                              for a  production  facility,  in  which  case,  at
                              Merck's sole option, Merck's obligations hereunder
                              shall be modified accordingly.

- --------------------------------------------------------------------------------
Direct Credit                 If financing  assistance is provided by means of a
Agreement:                    Direct  Credit,  the  parties  shall  negotiate  a
                              mutually satisfactory  construction loan agreement
                              with  usual  and   customary   terms  for  similar
                              agreements under comparable circumstances.

- --------------------------------------------------------------------------------
Guaranty:                     If  financing  assistance  is provided by means of
                              the  Guaranty,   the  parties  shall  negotiate  a
                              mutually   satisfactory  guaranty  agreement  with
                              usual and customary  terms for similar  agreements
                              under comparable  circumstances (including but not
                              limited to a reimbursement agreement).

- --------------------------------------------------------------------------------
Amount:                       Up to thirty million U.S. dollars ($30 million).

- --------------------------------------------------------------------------------
Maturity Date:                At a date certain, between the [ *** ] and [ *** ]
                              anniversary of the first drawdown.

- --------------------------------------------------------------------------------
Interest Rate:                If  financing  assistance  is provided by means of
                              Direct Credit, at an adjustable  interest rate per
                              annum equivalent to [ *** ].

- --------------------------------------------------------------------------------
Interest Payments:            If  financing  assistance  is provided by means of
                              Direct Credit, interest payments to Merck shall be
                              [ *** ] for the  term  of the  Notes,  payable  in
                              cash;  provided,   however,  that  interest  shall
                              accrue during the first [ *** ] quarters after the
                              issuance of the first Note and such interest, plus
                              compounded  interest  thereon,  shall  be due  and
                              payable on the last day of the [ *** ] quarter.

- --------------------------------------------------------------------------------
Principal Repayment:          [ *** ].

- --------------------------------------------------------------------------------
Drawdown Schedule:            [ *** ] delivers  written notice to Merck at least
                              10 days prior to any drawdown.

- --------------------------------------------------------------------------------
Use of Proceeds:              Planning,   development  and   construction  of  a
                              manufacturing  facility  in  conformity  with  the
                              production  concept,  including  the  purchase  of
                              related   

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                                       iii

<PAGE>

                              equipment, to produce the Compound,  Improvements,
                              Licensed   Products   and   Alternative   Licensed
                              Products and, subject to the prior approval of the
                              Steering Committee, other pharmaceutical products.

- --------------------------------------------------------------------------------
Security Interest:            As long as any Note shall remain  outstanding  and
                              prior to the maturity date, Merck shall retain the
                              senior  security  interest  in  the  manufacturing
                              facility,  including  but not limited to all plant
                              and  equipment,  and a  security  interest  in all
                              other assets of ImClone, including but not limited
                              to all of ImClone's patents,  trademarks and other
                              intellectual  property,  such that Merck  shall be
                              fully  secured with respect to the total amount of
                              the Direct Credit or Guaranty, as the case may be.

- --------------------------------------------------------------------------------
Change of Control:            Upon a change of  control of  ImClone,  (a) in the
                              case  of  a  Direct  Credit,  the  agreement  with
                              respect to which the Direct  Credit is provided to
                              ImClone  shall   terminate  and  all   outstanding
                              principal  and interest  shall become  immediately
                              due  and  payable,  or  (b)  in  the  case  of the
                              Guaranty,  the  Person  taking  control of ImClone
                              shall be  obligated,  as a condition to its taking
                              control, to cause the prompt release of Merck from
                              all of  Merck's  obligations  under the  Guaranty,
                              which  release  shall  occur no later than  thirty
                              (30)  calendar  days after the  effective  date of
                              such change of control.

- --------------------------------------------------------------------------------
Termination                   Upon the termination of the Agreement  pursuant to
of  Agreement:                Section 11.2, Section 11.5 (if such termination is
                              the  result  of  a  breach  of  the  Agreement  by
                              ImClone), Section 11.6, or Section 11.7, [ *** ].

                              Upon the termination of the Agreement  pursuant to
                              Section 11.4, [ *** ]. Upon the termination of the
                              Agreement pursuant to Section 11.3 or Section 11.5
                              (if such  termination is the result of a breach of
                              the Agreement by Merck), [ *** ].

                              Upon  the  termination  of the  Agreement  for any
                              reason  other  than  those  listed  in  the  three
                              paragraphs above, [ *** ].

                              Upon  the  termination  of the  Agreement  for any
                              reason,  in the case of a Guaranty,  ImClone shall
                              be obligated to use its best reasonable efforts to
                              cause  the  prompt  release  of Merck  from all of
                              Merck's obligations under the Guaranty.

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<PAGE>

                                   SCHEDULE A
                               DESCRIPTION OF C225

            C225 - Epidermal Growth Factor Receptor (EGFr) Inhibitor

The active substance is C225 chimeric monoclonal antibody, a chimerized antibody
of the IgG1 subclass,  derived from mouse hybridoma.  The chimerization  process
resulted in an IgG1 subclass antibody with binding affinity to EGFr and inhibits
EGF/TGF(alpha)  induced  activation of this tyrosine kinase receptor.  C225 also
will result in the stimulation of EGFr internalization, effectively removing the
receptor from the cell surface for interaction with the ligand.

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                                        v

<PAGE>

                                   SCHEDULE B
               C225 INTERNATIONAL PATENTS AND PATENT APPLICATIONS

[ *** ]

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                                       vi

<PAGE>

                                   SCHEDULE C
                   DEFINITION OF "FULLY LOADED COST OF GOODS"

[ *** ]

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                                       vii

<PAGE>

                                   SCHEDULE D
                        RESEARCH AND DEVELOPMENT PROTOCOL

[ *** ].

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<PAGE>

                                   SCHEDULE E
                               MILESTONE PAYMENTS

1. The Milestone Payments under Section 4.1 of the Agreement, subject to Section
11.3  thereof,  shall be made by  Merck  within  thirty  (30)  calendar  days of
ImClone's  fulfillment  of any given  Milestone  designated  on the charts below
(each, a  "Milestone"),  in the amounts  summarized  therein (each, a "Milestone
Payment  Date").  Such expected dates of achievement of Milestones  shall be set
promptly by the Steering Committee following the execution of the Agreement, and
this Schedule E shall be amended  accordingly.  On the  Milestone  Payment Dates
designated  below as  "Milestone  Payments  with Equity  Purchases"  (Milestones
designated  numbers 11 through 17 below),  ImClone shall issue  Acquired  Voting
Shares or, as provided in Section 4.1(b) of the Agreement,  Acquired  Non-Voting
Shares to Merck,  in each case at a per-share  purchase price  calculated in the
manner described below. The aggregate  purchase price shall be the amount of the
respective Milestone Payment.

2.   Conversion of Acquired Non-Voting Shares.

      (a) During the  Standstill  Period,  Acquired  Non-Voting  Shares shall be
convertible  into  shares of  Common  Stock,  on a  share-for-share  basis  (the
"Milestone  Conversion  Shares"),  to the extent that the  aggregate  beneficial
ownership  of  Common  Stock  of Merck  and its  Affiliates  (including  for the
purposes  of this  calculation,  all  shares of Common  Stock  that Merck or its
Affiliates  may have the right to acquire  upon the  conversion  of the Series A
Convertible Preferred Stock but not including the Common Stock that Merck or its
Affiliates  may have the  right  to  acquire  upon  conversion  of the  Acquired
Non-Voting  Shares)  does not exceed  19.9% of the total  outstanding  shares of
Common Stock,  on a primary basis on the date Merck  notifies  ImClone of its or
its  Affiliate's  intent  to  convert  such  Acquired   Non-Voting  Shares  (the
"Conversion Notification Date"); provided, however, that the Acquired Non-Voting
Shares shall be  convertible  only if the  Conversion  Notification  Date occurs
within five years of the date of the occurrence of the Milestone Payment Date to
which the Acquired Non-Voting Shares relate; and further, provided, that ImClone
shall not be  obligated  during  the  Standstill  Period to issue the  Milestone

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Conversion  Shares  if  such  issuance  would  cause  the  aggregate  beneficial
ownership  of Merck  and its  Affiliates  of  Common  Stock  (including  for the
purposes  of this  calculation,  all  shares of Common  Stock that Merck and its
Affiliates  may have the right to acquire  upon the  conversion  of the Series A
Convertible  Preferred  Stock but  excluding the Common Stock that Merck and its
Affiliates  may have the right to acquire  upon the  conversion  of the Acquired
Non-Voting  Shares) to exceed  19.9% of the total  outstanding  shares of Common
Stock on a primary basis as of the Conversion Notification Date.

      (b) After the termination of the Standstill  Period,  Acquired  Non-Voting
Shares  shall  be  freely   convertible  into  shares  of  Common  Stock,  on  a
share-for-share  basis;  provided,  however, that, with respect only to Acquired
Non-Voting  Shares that were acquired by Merck during the Standstill  Period, in
the event that  Merck  chooses to convert  such  Acquired  Non-Voting  Shares to
Milestone  Conversion  Shares after the termination of the Standstill Period and
Merck's  beneficial  ownership  of  Common  Stock  exceeds  19.9%  of the  total
outstanding  shares  of  Common  Stock on a  primary  basis  as of the  relevant
Conversion  Notification  Date,  by the  resolution  of  the  ImClone  Board  of
Directors,  Merck shall be obligated,  without prejudice to Merck's registration
rights pursuant to Schedule G of the Agreement,  to sell as soon as commercially
practicable the Milestone  Conversion  Shares it received upon such  conversion.

      (c) Merck agrees that in no event shall it make a disposition  directly or
indirectly  of any  Acquired  Non-Voting  Shares,  other than to an Affiliate of
Merck, unless it shall have first obtained the prior written consent of ImClone.

3. The  purchase  price of any  Acquired  Voting  Shares or Acquired  Non-Voting
Shares to be issued to Merck on any given  Milestone  Payment  Date  pursuant to
Section 4.1(a) and (b), respectively, of the Agreement and this Schedule E shall
be  calculated as follows:  On any given  Milestone  Payment Date,  the purchase
price of the Acquired Voting Shares or Acquired  Non-Voting  Shares shall be the
sum of:

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      (a) the average of the closing  prices of shares of Common Stock as traded
on  Nasdaq  (or if the  Common  Stock  is not  then  trading  on  Nasdaq  on any
securities exchange or national automated inter-dealer stock quotation system on
which shares of Common Stock at any given time are listed or quoted)  during the
preceding 30 trading days prior to such Milestone Payment Date and

      (b) a premium on such  30-day  average  share  price (the  "Average  Share
Price") to be calculated as follows:

            (i) If ImClone  achieves a  Milestone  on a date that is  designated
"Early" on the table  below,  the premium  shall be [ *** ]of the Average  Share
Price;

            (ii) If ImClone  achieves a Milestone  on a date that is  designated
"On Time" on the table below,  the premium shall be [ *** ] of the Average Share
Price; or

            (iii) If ImClone  achieves a Milestone on a date that is  designated
"Late" on the table  below,  the premium  shall be [ *** ] of the Average  Share
Price;

      provided,  however, that in determining whether a Milestone is achieved on
a date that is  designated  "Early,"  "On Time" or "Late,"  such dates  shall be
adjusted  forward to take account any delays  associated with activities  within
Merck's sole control.

4.  Notwithstanding  any other provision of this Agreement,  at least sixty (60)
calendar  days prior to any issuance of any  Acquired  Voting  Shares,  Acquired
Non-Voting Shares or Milestone Conversion Shares to Merck hereunder, counsel for
both parties  shall  determine  whether  such  issuance of shares to Merck or an
Affiliate of Merck will require any  notification  or any other action by either
party under the HSR Act, as then in effect.  The parties hereto shall  cooperate
with one another in good faith and, at their own expense,  take any  appropriate
actions,  execute any documents, and prepare and file any required notifications
under the HSR Act prior to the issuance of any Acquired Voting Shares,  Acquired
Non-Voting Shares or Milestone Conversion Shares to Merck or its Affiliates.  No
Acquired  Voting  Shares,  

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Acquired  Non-Voting  Shares or Milestone  Conversion  Shares shall be issued to
Merck or its Affiliates except in compliance with the applicable requirements of
the HSR Act.

[ *** ]

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<PAGE>

                                   SCHEDULE F
                  DESCRIPTION OF COLLATERAL LICENSE AGREEMENTS

Collateral License Agreements as follows:

License agreement to be entered into with [ *** ].

Sublicense rights in the Territory to [ *** ].

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                                   SCHEDULE G
                               REGISTRATION RIGHTS

1.   Demand Registration.

      (a) One time  during any  12-month  period,  Merck shall have the right to
make a written request for registration under the 1933 Act of all or part of the
Registrable  Securities  (a  "Demand  Registration");  provided,  however,  that
ImClone  shall  be  obligated  hereunder  to  make  no  more  than  four  Demand
Registrations in total. A registration shall not count as a Demand  Registration
until it has  become  effective.  If  Merck  so  elects,  the  offering  of such
Registrable Securities pursuant to such Demand Registration shall be in the form
of an  underwritten  offering.  Merck shall  select the  book-running  and other
managing  underwriters  in  connection  with such  offering  and any  additional
underwriters  or investment  bankers to be used in connection with the offering;
provided,  that such  underwriters  and  investment  bankers must be  reasonably
satisfactory  to ImClone.  Upon written  request of Merck in compliance with the
preceding  sentence that ImClone  effect  registration  with respect to all or a
part  of  the  Registrable  Securities,   ImClone  shall,  as  expeditiously  as
reasonably possible:

            (i) prepare and file within 45 days of such request for registration
with the  Commission  a  registration  statement  on Form S-3 or on any form for
which   ImClone  then   qualifies  or  which  counsel  for  ImClone  shall  deem
appropriate,  as the case may be, and which form shall be available for the sale
of the Registrable Securities;  provided, that before filing with the Commission
a registration statement or prospectus or any amendments or supplements thereto,
ImClone  shall (i) furnish to one counsel  selected by Merck  copies of all such
documents  proposed to be filed,  which documents shall be subject to reasonable
advance  review of such counsel,  and (ii) notify Merck of any stop order issued
or threatened by the  Commission  and take all  reasonable  actions  required to
prevent the entry of such stop order or to remove it if entered;

            (ii) keep such registration effective for a period of no longer than
two (2) years after the date of filing of such  registration  statement or until
Merck and/or its  Affiliates  have completed the  distribution  described in the
registration statement relating thereto, whichever first occurs;

            (iii)  prepare  and file with the  Commission  such  amendments  and
supplements  to  such  registration   statements  and  the  Prospectus  used  in
connection with such  registration  statement as may be necessary to comply with
the provisions of the 1933 Act with respect to the disposition of all securities
covered by such registration statement;

            (iv)  furnish  to Merck such  number of copies of such  registration
statement,  each  amendment and  supplement  thereto (in each case including all
exhibits  thereto),  the  Prospectus  included  in such  registration  statement
(including each preliminary prospectus),  in conformity with the requirements of
the 1933 Act and such other  documents as Merck may reasonably  request in order
to facilitate the disposition of the Registrable Securities;

            (v) advise  Merck and the  managing  underwriters,  if any,  and, if
requested by Merck or the managing underwriters,  if any, confirm such advice in
writing,  when a registration  statement or any amendment thereto has been filed
with the Commission and when the  registration  statement or any  post-effective
amendment thereto has become effective;

            (vi) use its best  efforts  to obtain  the  withdrawal  of any order
suspending the  effectiveness of any registration  statement,  or the lifting of
any suspension of the  qualification  (or 

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<PAGE>

exemption  from  qualification)  of the  Registrable  Securities for sale in any
jurisdiction, at the earliest possible time;

            (vii)  cause all such  Registrable  Securities  to be listed on each
securities  exchange  on which  similar  securities  issued by ImClone  are then
listed;

            (viii)   provide  a  transfer  agent  and  registrar  for  all  such
Registrable  Securities not later than the effective  date of such  registration
statement;

            (ix) immediately notify Merck at any time when a Prospectus relating
thereto is required to be delivered  under the 1933 Act, of the happening of any
event  as a  result  of  which  the  Prospectus  included  in such  registration
statement  contains an untrue statement of a material fact or omits to state any
material fact required to be stated  therein or necessary to make the statements
therein not misleading in light of the  circumstances  then existing,  and shall
promptly  prepare  and  furnish  to  Merck a  supplement  or  amendment  to such
Prospectus so that, as thereafter delivered to the purchasers of the Registrable
Securities,  such Prospectus shall not contain an untrue statement of a material
fact or omit to state  any  material  fact  required  to be  stated  therein  or
necessary  to make  the  statements  therein  not  misleading  in  light  of the
circumstances then existing;

            (x)  make  available  for  inspection  by  Merck,   any  underwriter
participating in any disposition  pursuant to such registration  statement,  and
any attorney,  accountant or other agent retained by Merck, its Affiliates or an
underwriter (collectively,  the "Inspectors"),  all financial and other records,
pertinent  corporate  documents  and  properties of ImClone  (collectively,  the
"Records") as shall be reasonably necessary to enable them to exercise their due
diligence responsibility,  and cause ImClone's officers, directors and employees
to  supply  all  information  reasonably  requested  by any such  Inspectors  in
connection  with  such  registration  statement;  provided,  however,  that such
Inspectors  shall first agree in writing  with ImClone that any Records that are
reasonably and in good faith  designated by ImClone as  confidential at the time
of delivery of such Records shall be kept  confidential by such Inspectors;  and
in connection with  underwritten  offerings,  use its reasonable best efforts to
obtain a  comfort  letter  from  ImClone's  independent  public  accountants  in
customary  form and  covering  such matters of the type  customarily  covered by
comfort  letters as Merck  reasonably  requests.  

      (b) Merck  agrees  that,  upon  receipt of any notice from  ImClone of the
happening  of any  event of the  kind  described  in  Section  1(a)(ix)  of this
Schedule  G,  Merck  shall  forthwith  discontinue  disposition  of  Registrable
Securities  pursuant to the  registration  statement  covering such  Registrable
Securities  until Merck's  receipt of the copies of the  supplemented or amended
Prospectus  contemplated  by Section  1(a)(ix)  of this  Schedule  G, and, if so
directed by ImClone,  Merck shall deliver to ImClone (at ImClone's  expense) all
copies,  other than  permanent  file copies then in Merck's  possession,  of the
Prospectus  covering such Registrable  Securities current at the time of receipt
of such notice.

      (c) Holdback Agreements. Merck agrees not to offer, sell, contract to sell
or otherwise dispose of any Common Stock, or any securities  convertible into or
exchangeable  or exercisable for such  securities,  during the 14 days prior to,
and  during  the  90-day  period   beginning  on,  the  effective  date  of  any
registration  statement  registering  Registrable  Securities other than (a) the
Registrable Securities to be sold pursuant to such registration  statement,  (b)
any shares of Common Stock sold upon the exercise of an option or warrant or the
conversion of a security  outstanding  at such date and (c) if and to the extent
permitted by applicable law, and the managing underwriter or underwriters in the
case of an underwritten  public  offering,  in a private  placement  exempt from
registration under the 1933 Act.

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2. Piggyback Registration.  If ImClone proposes to file a registration statement
under  the 1933 Act with  respect  to an  offering  by  ImClone  of any class of
securities  after the Closing Date (other than a registration  statement on Form
S-4 or S-8 or any successor  form to such Forms,  or filed in connection  with a
merger,  exchange  offer or an offering  of  securities  solely to the  existing
stockholders  in  connection  with a rights  offering or solely to  employees of
ImClone),  then ImClone  shall give written  notice of such  proposed  filing to
Merck at least twenty days before the  anticipated  filing date, and such notice
shall  offer  Merck the  opportunity  to  register  such  amount of  Registrable
Securities as Merck may request. ImClone shall use its best efforts to cause the
managing  underwriter or  underwriters  of a proposed  underwritten  offering to
permit Merck to include such  securities  in such offering on the same terms and
conditions   as  any   similar   securities   of   ImClone   included   therein.
Notwithstanding the foregoing,  (i) if the managing  underwriter or underwriters
of such proposed  underwritten  offering delivers a written notice to Merck that
the total amount of securities  which Merck and its Affiliates,  ImClone and any
other  Persons or entities  (other than such other Persons or entities with whom
ImClone has agreements on the date hereof prohibiting reduction or limitation as
contemplated  herein)  having  registration  rights,  intend to  include in such
offering is sufficiently large as to materially and adversely affect the success
of such  offering,  then the amount of securities to be offered for the accounts
of Merck and its  Affiliates  and for the  accounts  of such  other  Persons  or
entities shall be reduced or limited in proportion to their  respective  amounts
of securities  to the extent  necessary to reduce the total amount of securities
to be  included  in such  offering to the amount  recommended  by such  managing
underwriter;  provided,  that no reduction shall be made in the securities to be
offered  for the  account of  ImClone;  and (ii) if such  proposed  underwritten
offering  involves  only  equity  securities  and the  managing  underwriter  or
underwriters  thereof  shall have  delivered a written  notice to Merck that the
inclusion of any  Registrable  Securities in such offering will  materially  and
adversely  affect the success of such offering,  then no Registrable  Securities
shall be included in such offering.

3. Expenses of Registration.

      All Registration  Expenses  incurred in connection with any  registration,
qualification or compliance  pursuant to Section 1 or Section 2 of this Schedule
G shall be borne by ImClone.  All Selling  Expenses  relating to  securities  so
registered shall be borne by Merck.

4. Indemnification.

      (a)  Indemnification by ImClone.  ImClone shall, and it hereby does, agree
to indemnify and hold harmless,  to the full extent  permitted by law, Merck and
its  Affiliates  and their  respective  directors  and  officers  and each other
Person,  if any,  who  controls  Merck within the meaning of the 1933 Act or the
Exchange Act, against any and all losses, claims, damages or liabilities,  joint
or  several,  and  expenses  (including  any  amounts  Personally  paid  in  any
settlement)  to which Merck or its Affiliates or any such director or officer or
controlling  Person  may  become  subject  under  the 1933  Act,  common  law or
otherwise, insofar as such losses, claims, damages or liabilities (or actions or
proceedings  in respect  thereof) or expenses arise out of or are based upon (i)
any untrue  statement or alleged untrue statement of any material fact contained
in any registration  statement under which such securities were registered under
the 1933 Act, any preliminary, final or summary prospectus contained therein, or
any amendment or supplement thereto, or (ii) any omission or alleged omission to
state therein a material fact required to be stated therein or necessary to make
the statements therein not misleading,  and ImClone shall reimburse Merck or its
Affiliates and each such director,  officer or controlling  Person for any legal
or  any  other  expenses   reasonably   incurred  by  them  in  connection  with
investigating or defending such loss, claim,  liability,  action or proceedings;
provided,  that ImClone  shall not be liable in any such case to the extent that
any such loss,  claim,  damage,  liability  (or action or  proceeding in respect
thereof)  or  expenses  arises out of or is based upon any untrue  statement  or
alleged  untrue   statement  or  omission  or  alleged  omission  made  in  such
registration  statement  or  amendment  or  supplement  thereto  or in any  such
preliminary, final

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or  summary   prospectus  in  reliance  upon  and  in  conformity  with  written
information  furnished  to  ImClone  by Merck or its  Affiliates  for use in the
preparation thereof; and provided,  further, that ImClone shall not be liable to
Merck or its Affiliates or any other Person,  if any, who controls Merck,  under
the  indemnity  agreement in this  Section 4(a) with respect to any  preliminary
prospectus as amended or supplemented as the case may be, to the extent that any
such loss,  claim,  damage or liability of Merck,  its Affiliates or controlling
Person  results  from the fact that  Merck or its  Affiliates  sold  Registrable
Securities  to a Person to whom there was not sent or given,  at or prior to the
written confirmation of such sale, a copy of the final prospectus (including any
documents  incorporated  by reference  therein),  whichever  is most recent,  if
ImClone has previously  furnished copies thereof to Merck and its Affiliates and
such final prospectus,  as then amended or supplemented,  has corrected any such
misstatement  or omission.  Such indemnity shall remain in full force and effect
regardless of any investigation  made by or on behalf of Merck or its Affiliates
or any such  director,  officer  or  controlling  Person and shall  survive  the
transfer of such  securities by Merck or its  Affiliates.  It is agreed that the
indemnity  agreement  contained  in this Section 4(a) shall not apply to amounts
paid in settlement of any such loss, claim, damage, liability, or action if such
settlement  is effected  without the consent of ImClone  (which  consent has not
been unreasonably withheld).

      (b)  Indemnification by Merck. Merck shall, if the Registrable  Securities
are included in the securities as to which such registration,  qualification, or
compliance  is being  effected,  indemnify and hold harmless (in the same manner
and to the same  extent  as set  forth in  subdivision  (a) of this  Section  4)
ImClone,  any underwriter and their  respective  controlling  Persons within the
meaning of the 1933 Act and the Exchange Act, and all other prospective  sellers
and their  respective  controlling  Persons  with  respect to any  statement  or
alleged  statement  in or omission or alleged  omission  from such  registration
statement,  any preliminary,  final or summary prospectus  contained therein, or
any amendment or supplement,  if such statement or alleged statement or omission
or alleged  omission was made in reliance  upon and in  conformity  with written
information  furnished  to  ImClone  by Merck or its  Affiliates  for use in the
preparation  of such  registration  statement,  preliminary,  final  or  summary
prospectus or amendment or supplement,  or a document  incorporated by reference
into any of the foregoing.  Such indemnity shall remain in full force and effect
regardless  of  any  investigation  made  by or on  behalf  of  ImClone  or  any
underwriter  or any  of  Merck  or its  Affiliates  or any of  their  respective
directors,  officers and  controlling  Persons and shall survive the transfer of
such  securities  by  Merck  or its  Affiliates;  provided,  however,  that  the
obligations of Merck  hereunder shall not apply to amounts paid in settlement of
any such claims, losses, damages, or liabilities (or actions in respect thereof)
if such settlement is effected without the consent of Merck (which consent shall
not be unreasonably withheld).

      (c) Notices of Claims,  Etc. Each party entitled to indemnification  under
this Section 4 (the "Indemnified Party") shall give notice to the party required
to  provide  indemnification  (the  "Indemnifying  Party")  promptly  after such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought,  and shall permit the  Indemnifying  Party to assume the defense of such
claim or any  litigation  resulting  therefrom,  provided,  that counsel for the
Indemnifying  Party,  who  shall  conduct  the  defense  of  such  claim  or any
litigation  resulting  therefrom,  shall be  approved by the  Indemnified  Party
(whose approval shall not unreasonably be withheld),  and the Indemnified  Party
may participate in such defense at such party's expense, and provided,  further,
that the failure of any  Indemnified  Party to give  notice as  provided  herein
shall not relieve the Indemnifying  Party of its obligations  under this Section
4, to the extent such failure is not prejudicial.  No Indemnifying Party, in the
defense of any such claim or litigation,  shall, except with the consent of each
Indemnified Party, consent to entry of any judgment or enter into any settlement
that  does not  include  as an  unconditional  term  thereof  the  giving by the
claimant or plaintiff to such Indemnified  Party of a release from all liability
in respect to such claim or  litigation.  Each  Indemnified  Party shall furnish
such  information  regarding  itself or the claim in question as an Indemnifying
Party may reasonably  request in writing and as shall be reasonably  required in
connection with defense of such claim and litigation  resulting  therefrom.  

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      (d) Contribution. If the indemnification provided for in this Section 4 is
held by a court of competent  jurisdiction  to be  unavailable to an Indemnified
Party with respect to any loss, liability, claim, damage, or expense referred to
therein,  then the Indemnifying  Party, in lieu of indemnifying such Indemnified
Party  hereunder,  shall  contribute  to the  amount  paid  or  payable  by such
Indemnified Party as a result of such loss, liability, claim, damage, or expense
in such  proportion  as is  appropriate  to reflect  the  relative  fault of the
Indemnifying  Party on the one hand and of the Indemnified Party on the other in
connection  with  the  statements  or  omissions  that  resulted  in such  loss,
liability,  claim,  damage,  or expense as well as any other relevant  equitable
considerations.  The  relative  fault  of  the  Indemnifying  Party  and  of the
Indemnified  Party shall be  determined  by reference  to,  among other  things,
whether  the  untrue or alleged  untrue  statements  of a  material  fact or the
omission  to state a  material  fact  relates  to  information  supplied  by the
Indemnifying Party or by the Indemnified Party and the parties' relative intent,
knowledge,  access to  information,  and  opportunity to correct or prevent such
statement or omission.

5. Miscellaneous.

      (a) Rule 144. ImClone covenants that it shall file any reports required to
be filed by it under  the 1933 Act and the 1934 Act and that it shall  take such
further action as Merck may reasonably request,  all to the extent required from
time to time, to enable Merck and its Affiliates to sell Registrable  Securities
without  registration under the 1933 Act within the limitation of the exemptions
provided by Rule 144 under the 1933 Act,  as such Rule may be amended  from time
to time, or any similar rule or regulation  hereafter adopted by the Commission.
Upon the request of Merck, ImClone shall deliver to Merck a written statement as
to whether it has complied with such requirements.

      (b) Other Registration Rights. Except as provided hereunder,  for a period
of six months from and after the date of the Agreement,  ImClone shall not grant
to any other  Person the right to  request  ImClone to  register  securities  of
ImClone without the prior written  consent of Merck,  which consent shall not be
unreasonably withheld.

      (c) Assignability of Registration Rights. The registration rights afforded
Merck  and  its  Affiliates  herein  shall  be  assignable  to a  transferee  of
Registrable  Securities  from Merck or any of its Affiliates so long as (i) such
transferee has acquired no fewer than 800,000  shares of Registrable  Securities
(as adjusted  from time to time to reflect  stock  splits,  stock  dividends and
similar  changes  in the  capitalization  of  ImClone)  from Merck or any of its
Affiliates,  (ii) such  transferee  has agreed with ImClone in writing to comply
with all  applicable  provisions  hereof and (iii) Merck has otherwise  complied
with all provisions hereof that affect its right to sell,  transfer or otherwise
dispose of shares of Registrable  Securities;  provided,  however,  that ImClone
shall not be  required  to  effect  more than one  registration  of  Registrable
Securities  in  any  12-month  period  or  more  than a  total  of  four  Demand
Registrations under this Schedule G. For a transfer of registration rights to be
effective,  Merck shall give ImClone written notice at the time of such transfer
stating the name and address of the transferee and  identifying  the shares with
respect to which the rights under this Section 5(c) are being assigned.

      (d) This  Schedule  G shall  supercede  Sections  7, 8, 9, 10 and 11of the
Preferred Stock Purchase  Agreement,  which Sections 7, 8, 9, 10 and 11 shall be
of no further effect. 

6. Definitions.

      As used in this Schedule G:

      (a) The term  "Commission"  shall mean the U.S.  Securities  and  Exchange
Commission or any other federal agency at the time administering the 1933 Act or
the 1934 Act.

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      (b) The term "Person" shall mean an individual, partnership,  corporation,
limited liability company, trust,  unincorporated  organization or government or
political department or agency thereof or other entity.

      (c) The term  "Prospectus"  shall  mean  the  prospectus  included  in any
Registration  Statement  (including,   without  limitation,  a  prospectus  that
discloses  information  previously omitted from a prospectus filed as part of an
effective registration statement in reliance upon Rule 430A under the 1933 Act),
as amended or  supplemented  by any prospectus  supplement,  with respect to the
terms of the offering of any portion of Registrable Securities,  covered by such
Registration  Statement,  and all amendments and  supplements to the Prospectus,
including post-effective  amendments, and all material incorporated by reference
into such Prospectus.

      (d) The term  "Registrable  Securities"  shall  mean any and all  Acquired
Voting Shares,  Milestone  Conversion Shares,  and "Conversion  Shares" (as such
term is defined in Section 1 of the Preferred Stock Purchase  Agreement).  As to
any  Registrable  Securities,  such  securities  shall  cease to be  Registrable
Securities  when (i) a  registration  statement with respect to the sale of such
securities  shall have become  effective  under the 1933 Act and such securities
shall have been disposed of pursuant to such effective  registration  statement,
(ii) such  securities  shall have been  distributed  pursuant to Rule 144,  Rule
144A, or any similar  provision  then in force,  under the 1933 Act,  (iii) such
securities  shall have been otherwise  transferred,  new  certificates  or other
evidences  of  ownership  for them not  bearing  a  legend  restricting  further
transfer and not subject to any stop  transfer  order or other  restrictions  on
transfer shall have been delivered by ImClone and subsequent disposition of such
securities  shall not require  registration or  qualification of such securities
under the 1933 Act or any state  securities  laws then in force or (iv) the sale
of  such  securities  by  Merck  or  its  Affiliates  shall  no  longer  require
registration   under  the  1933  Act  or  such  securities  shall  cease  to  be
outstanding.

      (e) The terms "register," "registered" and "registration" shall refer to a
registration  effected  by  preparing  and filing a  registration  statement  in
compliance  with  the  1933  Act  and  the  applicable   rules  and  regulations
thereunder,  and  the  declaration  or  ordering  of the  effectiveness  of such
registration statement.

      (f) The term  "Registration  Expenses" shall mean all expenses incurred in
effecting  any  registration  pursuant  to  this  Agreement,  including  without
limitation, all registration,  qualification and filing fees, printing expenses,
escrow fees, fees and  disbursements  of counsel for ImClone,  blue sky fees and
expenses and expenses of any regular or special  audits  incident to or required
by any such registration, but shall not include Selling Expenses.

      (g) The term "Selling Expenses" shall mean all underwriting  discounts and
selling  commissions  applicable to the sale of the  Registrable  Securities and
fees  and   disbursements  of  counsel  for  Merck  (other  than  the  fees  and
disbursements  of counsel  constituting a part of blue sky fees and expenses and
included in Registration Expenses).

*** - Confidential Treatment Requested


                                       xix

<PAGE>

                                   SCHEDULE H
                           FORM OF OPINIONS OF COUNSEL

1. Upon the execution of the Agreement, an opinion letter of the general counsel
of ImClone, in form and content satisfactory to Merck, shall be addressed to and
delivered  to Merck and  dated as of the  execution  date,  which  letter  shall
provide substantially as follows:

      (a) ImClone is a corporation  duly  incorporated,  validly existing and in
good standing under the laws of the State of Delaware.

      (b) The  execution,  delivery and  performance by ImClone of the Agreement
are  within  ImClone's  corporate  powers and have been duly  authorized  by all
necessary corporate action on the part of ImClone.  The Agreement  constitutes a
valid and binding  agreement  of ImClone,  enforceable  in  accordance  with its
terms,  subject  to  (i)  bankruptcy,   insolvency  or  similar  laws  affecting
creditors'  rights generally,  (ii) general  equitable  principles and (iii) the
Exon-Florio Act, Section 721 of Title VII of the Defense Production Act of 1950,
as amended, and the rules and regulations promulgated thereunder.

      (c) The  execution,  delivery and  performance by ImClone of the Agreement
require no action by or in respect of, or  declaration  to or filing  with,  any
governmental body, agency,  official or authority other than compliance with (i)
any applicable  requirements of the Securities  Exchange Act of 1934, as amended
(the "1934 Act") and state  securities or "blue sky" laws,  (ii) any  applicable
requirements  of Delaware law,  (iii) the rules and  regulations of the National
Association  of  Securities  Dealers and the Nasdaq Stock  Market,  and (iv) any
applicable  requirements of the Hart-Scott-Rodino  Antitrust Improvements Act of
1976, as amended, and the rules and regulations promulgated thereunder (the "HSR
Act").

      (d) The execution, delivery and performance by ImClone of the Agreement do
not  and  will  not  (i)   contravene  or  conflict  with  the   certificate  of
incorporation  or  bylaws  of  ImClone;  (ii)  contravene  or  conflict  with or
constitute  a  violation  of any  provision  of any law,  regulation,  judgment,
injunction,  order or  decree  binding  upon or  applicable  to  ImClone;  (iii)
contravene, conflict with, constitute a breach of or default under, or give rise
to any  right of  termination,  cancellation  or  acceleration  of any  right or
obligation of ImClone under,  any provision of any agreement,  contract or other
instrument  binding upon ImClone or any of its  properties or (iv) result in the
creation or  imposition  of any lien,  encumbrance  of claim of ownership of any
kind by any  third  party on any  asset,  whether  tangible  or  intangible,  of
ImClone.

2. With respect to each delivery of Acquired Voting Shares,  Acquired Non-Voting
Shares or Milestone  Conversion  Shares to Merck, as the case may be, an opinion
letter of the general  counsel of ImClone,  in form and content  satisfactory to
Merck,  shall  be  addressed  to and  delivered  to Merck  and  dated as of such
delivery date, which letter shall provide substantially as follows:

      (a) ImClone is a corporation  duly  incorporated,  validly existing and in
good standing under the laws of the State of Delaware.

      (b) The  execution,  delivery and  performance by ImClone of the Agreement
are  within  ImClone's  corporate  powers and have been duly  authorized  by all
necessary corporate action on the part of ImClone.  The Agreement  constitutes a
valid and binding  agreement  of ImClone,  enforceable  in  accordance  with its
terms,  subject  to  (i)  bankruptcy,   insolvency  or  similar  laws  affecting
creditors'  rights 

*** - Confidential Treatment Requested


                                       xx

<PAGE>

generally,  (ii) general  equitable  principles and (iii) the  Exon-Florio  Act,
Section 721 of Title VII of the Defense Production Act of 1950, as amended,  and
the rules and regulations promulgated thereunder.

      (c) The [Acquired Voting Shares] [Acquired  Non-Voting  Shares] [Milestone
Conversion  Shares] are validly issued,  fully paid and  non-assessable and free
and clear of any and all liens, encumbrances and claims of ownership of any kind
of any third party and free of preemptive or similar  rights.  Based only on the
market price of the Common Stock as of the date of the  Agreement,  a sufficient
number of shares of Common  Stock has been  authorized  and reserved for Merck's
acquisition of Acquired Voting Shares and Milestone  Conversion  Shares pursuant
to the Agreement.

      (d) The  execution,  delivery and  performance by ImClone of the Agreement
require no action by or in respect of, or  declaration  to or filing  with,  any
governmental body, agency,  official or authority other than compliance with (i)
any applicable  requirements of the 1934 Act and state  securities or "blue sky"
laws,  (ii) any  applicable  requirements  of Delaware law,  (iii) the rules and
regulations  of the National  Association  of Securities  Dealers and the Nasdaq
Stock Market,  and (iv) any  applicable  requirements  of the  Hart-Scott-Rodino
Antitrust  Improvements  Act of 1976, as amended,  and the rules and regulations
promulgated thereunder (the "HSR Act").

      (e) The execution, delivery and performance by ImClone of the Agreement do
not  and  will  not  (i)   contravene  or  conflict  with  the   certificate  of
incorporation  or  bylaws  of  ImClone;  (ii)  contravene  or  conflict  with or
constitute  a  violation  of any  provision  of any law,  regulation,  judgment,
injunction,  order or  decree  binding  upon or  applicable  to  ImClone;  (iii)
contravene, conflict with, constitute a breach of or default under, or give rise
to any  right of  termination,  cancellation  or  acceleration  of any  right or
obligation of ImClone under,  any provision of any agreement,  contract or other
instrument  binding upon ImClone or any of its  properties or (iv) result in the
creation or  imposition  of any lien,  encumbrance  of claim of ownership of any
kind by any  third  party on any  asset,  whether  tangible  or  intangible,  of
ImClone.

*** - Confidential Treatment Requested


                                       xxi



                                                                    Exhibit 23.1

                              Accountants' Consent

The Board of Directors
Imclone Systems Incorporated:

We consent to the use of our report incorporated herein by reference.

Princeton, New Jersey
January 8, 1999

                                                             /s/ KPMG LLP



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