<PAGE>   1


                                                                   EXHIBIT 10.75
                                      NOTE

         THIS NOTE HAS NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES
ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), OR ANY STATE SECURITIES LAWS,
AND, ACCORDINGLY, MAY NOT BE OFFERED OR SOLD WITHIN THE UNITED STATES OR TO, OR
FOR THE ACCOUNT OR BENEFIT OF, U.S. PERSONS EXCEPT AS SET FORTH IN THE FOLLOWING
SENTENCE. BY ITS ACQUISITION HEREOF, THE HOLDER (1) REPRESENTS THAT (A) IT IS A
"QUALIFIED INSTITUTIONAL BUYER" (AS DEFINED IN RULE 144A UNDER THE SECURITIES
ACT) OR (B) IT IS AN INSTITUTIONAL "ACCREDITED INVESTOR" (AS DEFINED IN RULE
501(A)(1), (2), (3) OR (7) UNDER THE SECURITIES ACT) ("INSTITUTIONAL ACCREDITED
INVESTOR"); (2) AGREES THAT IT WILL NOT, PRIOR TO EXPIRATION OF THE HOLDING
PERIOD APPLICABLE TO SALES OF THIS NOTE UNDER RULE 144(K) UNDER THE SECURITIES
ACT (OR ANY SUCCESSOR PROVISION), RESELL OR OTHERWISE TRANSFER THIS NOTE OR THE
COMMON STOCK ISSUABLE UPON CONVERSION OF SUCH NOTE EXCEPT (A) TO IMCLONE SYSTEMS
INCORPORATED OR ANY SUBSIDIARY THEREOF, (B) INSIDE THE UNITED STATES TO A
QUALIFIED INSTITUTIONAL BUYER IN COMPLIANCE WITH RULE 144A UNDER THE SECURITIES
ACT, (C) INSIDE THE UNITED STATES TO AN INSTITUTIONAL ACCREDITED INVESTOR THAT,
PRIOR TO SUCH TRANSFER, FURNISHES TO THE BANK OF NEW YORK, AS TRUSTEE (OR A
SUCCESSOR TRUSTEE, AS APPLICABLE), A SIGNED LETTER CONTAINING CERTAIN
REPRESENTATIONS AND AGREEMENTS RELATING TO THE RESTRICTIONS ON TRANSFER OF THIS
NOTE (THE FORM OF WHICH LETTER CAN BE OBTAINED FROM SUCH TRUSTEE OR A SUCCESSOR
TRUSTEE, AS APPLICABLE), AND IF SUCH TRANSFER IS IN RESPECT OF AN AGGREGATE
PRINCIPAL AMOUNT OF NOTES OF LESS THAN $100,000, AN OPINION OF COUNSEL
ACCEPTABLE TO THE COMPANY THAT SUCH TRANSFER IS IN COMPLIANCE WITH THE
SECURITIES ACT, (D) OUTSIDE THE UNITED STATES IN COMPLIANCE WITH RULE 904 UNDER
THE SECURITIES ACT, (E) PURSUANT TO THE EXEMPTION FROM REGISTRATION PROVIDED BY
RULE 144 UNDER THE SECURITIES ACT (IF AVAILABLE) OR (F) PURSUANT TO A
REGISTRATION STATEMENT WHICH HAS BEEN DECLARED EFFECTIVE UNDER THE SECURITIES
ACT (AND WHICH CONTINUES TO BE EFFECTIVE AT THE TIME OF SUCH TRANSFER); (3)
PRIOR TO SUCH TRANSFER (OTHER THAN A TRANSFER PURSUANT TO CLAUSE (2)(F) ABOVE),
IT WILL FURNISH TO THE BANK OF NEW YORK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS
APPLICABLE), SUCH CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS THE
TRUSTEE MAY REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE
PURSUANT TO AN EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE
REGISTRATION REQUIREMENTS OF THE SECURITIES ACT; AND (4) AGREES THAT IT WILL
DELIVER TO EACH PERSON TO WHOM THIS NOTE IS TRANSFERRED A NOTICE SUBSTANTIALLY
TO THE EFFECT OF THIS LEGEND. IN CONNECTION WITH ANY TRANSFER OF THIS NOTE PRIOR
TO THE EXPIRATION OF THE HOLDING PERIOD APPLICABLE TO SALES OF THIS NOTE
<PAGE>   2

UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY SUCCESSOR PROVISION), THE
HOLDER MUST CHECK THE APPROPRIATE BOX SET FORTH ON THE REVERSE HEREOF RELATING
TO THE MANNER OF SUCH TRANSFER AND SUBMIT THIS CERTIFICATE TO THE BANK OF NEW
YORK AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE). IF THE PROPOSED
TRANSFEREE IS AN INSTITUTIONAL ACCREDITED INVESTOR OR IS A PURCHASER WHO IS NOT
A U.S. PERSON, THE HOLDER MUST, PRIOR TO SUCH TRANSFER, FURNISH TO THE BANK OF
NEW YORK, AS TRUSTEE (OR A SUCCESSOR TRUSTEE, AS APPLICABLE), SUCH
CERTIFICATIONS, LEGAL OPINIONS OR OTHER INFORMATION AS SUCH TRUSTEE MAY
REASONABLY REQUIRE TO CONFIRM THAT SUCH TRANSFER IS BEING MADE PURSUANT TO AN
EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION
REQUIREMENTS OF THE SECURITIES ACT. THIS LEGEND WILL BE REMOVED UPON THE EARLIER
OF THE TRANSFER OF THIS NOTE PURSUANT TO CLAUSE (2)(F) ABOVE OR UPON ANY
TRANSFER OF THIS NOTE UNDER RULE 144(K) UNDER THE SECURITIES ACT (OR ANY
SUCCESSOR PROVISION). AS USED HEREIN, THE TERMS "UNITED STATES" AND "U.S.
PERSON" HAVE THE MEANINGS GIVEN TO THEM BY REGULATION S UNDER THE SECURITIES
ACT. THE INDENTURE CONTAINS A PROVISION REQUIRING THE TRUSTEE TO REFUSE TO
REGISTER ANY TRANSFER OF THIS NOTE IN VIOLATION OF THE FOREGOING RESTRICTION.
<PAGE>   3


                          IMCLONE SYSTEMS INCORPORATED

                   5 1/2% CONVERTIBLE SUBORDINATED NOTE DUE 2005

                                                                CUSIP: 45245WAB5

No.  P-1

         ImClone Systems Incorporated, a corporation duly organized and validly
existing under the laws of the State of Delaware (herein called the "Company",
which term includes any successor corporation under the Indenture referred to on
the reverse hereof), for value received hereby promises to pay to Morgan Stanley
& Co. Incorporated or its registered assigns, the principal sum of One Hundred
Thousand Dollars ($100,000) on March 1, 2005, at the office or agency of the
Company maintained for that purpose in accordance with the terms of the
Indenture, in such coin or currency of the United States of America as at the
time of payment shall be legal tender for the payment of public and private
debts, and to pay interest, semi-annually on March 1 and September 1 of each
year, commencing September 1, 2000, on said principal sum at said office or
agency, in like coin or currency, at the rate per annum of 5 1/2%, from March 1
or September 1, as the case may be, next preceding the date of this Note to
which interest has been paid or duly provided for, unless the date hereof is a
date to which interest has been paid or duly provided for, in which case from
the date of this Note, or unless no interest has been paid or duly provided for
on the Notes, in which case from February 29, 2000, until payment of said
principal sum has been made or duly provided for. Notwithstanding the foregoing,
if the date hereof is after any February 15 or August 15, as the case may be,
and before the following March 1 or September 1, this Note shall bear interest
from such March 1 or September 1; provided, however, that if the Company shall
default in the payment of interest due on such March 1 or September 1, then this
Note shall bear interest from the next preceding March 1 or September 1 to which
interest has been paid or duly provided for or, if no interest has been paid or
duly provided for on such Note, from February 29, 2000. Except as otherwise
provided in the Indenture, the interest payable on the Note pursuant to the
Indenture on any March 1 or September 1 will be paid to the Person entitled
thereto as it appears in the Note register at the close of business on the
record date, which shall be the February 15 or August 15 (whether or not a
Business Day) next preceding such March 1 or September 1, as provided in the
Indenture; provided, however, that any such interest not punctually paid or duly
provided for shall be payable as provided in the Indenture. Interest may, at the
option of the Company, be paid either (i) by check mailed to the registered
address of such Person (provided that the holder of Notes with an aggregate
principal amount in excess of $2,000,000 shall, at the written election of such
holder, be paid by wire transfer of immediately available funds) or (ii) by
transfer to an account maintained by such Person located in the United States;
provided, however, that payments to the Depositary will be made by wire transfer
of immediately available funds to the account of the Depositary or its nominee.


         Reference is made to the further provisions of this Note set forth on
the reverse hereof, including, without limitation, provisions subordinating the
payment of principal of and premium,

                                       1
<PAGE>   4
if any, and interest on the Notes to the prior payment in full of all Senior
Indebtedness, as defined in the Indenture, and provisions giving the holder of
this Note the right to convert this Note into Common Stock of the Company on the
terms and subject to the limitations referred to on the reverse hereof and as
more fully specified in the Indenture. Such further provisions shall for all
purposes have the same effect as though fully set forth at this place.

         This Note shall be deemed to be a contract made under the laws of the
State of New York, and for all purposes shall be construed in accordance with
and governed by the laws of the State of New York, without regard to principles
of conflicts of laws.

         This Note shall not be valid or become obligatory for any purpose until
the certificate of authentication hereon shall have been manually signed by the
Trustee or a duly authorized authenticating agent under the Indenture.

         IN WITNESS WHEREOF, the Company has caused this Note to be duly
executed.

                                         IMCLONE SYSTEMS INCORPORATED


                                         By:    /s/ Samuel D. Waksal
                                                -------------------------
                                         Name:      Samuel D. Waksal
                                                -------------------------
                                         Title:   President & CEO
                                               ---------------------------

Attest:  /s/ Carl S. Goldfischer
        ------------------------
Name:    Carl S. Goldfischer
        ------------------------
Title:   Vice President, Finance & CEO
         -----------------------------
Dated:   February 29, 2000
         -----------------------------

                                       2
<PAGE>   5
TRUSTEE'S CERTIFICATE OF AUTHENTICATION

This is one of the Notes described in the within-named Indenture.

THE BANK OF NEW YORK, as Trustee

By:  /s/ Robert A. Massimillo
     ------------------------
         Authorized Signatory


                                       3
<PAGE>   6
                          IMCLONE SYSTEMS INCORPORATED

                   5 1/2% CONVERTIBLE SUBORDINATED NOTE DUE 2005


         This Note is one of a duly authorized issue of Notes of the Company,
designated as its 5 1/2% Convertible Subordinated Notes due 2005 (herein called
the "Notes"), limited to the aggregate principal amount of $200,000,000
($240,000,000, if the option is fully exercised by the Initial Purchasers) all
issued or to be issued under and pursuant to an Indenture dated as of February
29, 2000 (herein called the "Indenture"), between the Company and The Bank of
New York, as trustee (herein called the "Trustee"), to which Indenture and all
indentures supplemental thereto reference is hereby made for a description of
the rights, limitations of rights, obligations, duties and immunities thereunder
of the Trustee, the Company and the holders of the Notes.

         In case an Event of Default (as defined in the Indenture) shall have
occurred and be continuing, the principal of, premium, if any, and accrued
interest (including Liquidated Damages (as defined in the Registration Rights
Agreement), if any) on all Notes may be declared by either the Trustee or the
holders of not less than 25% in aggregate principal amount of the Notes then
outstanding, and upon said declaration shall become, due and payable, in the
manner, with the effect and subject to the conditions provided in the Indenture.

         The Indenture contains provisions permitting the Company and the
Trustee, with the consent of the holders of not less than a majority in
aggregate principal amount of the Notes at the time outstanding, to execute
supplemental indentures adding any provisions to or changing in any manner or
eliminating any of the provisions of the Indenture or of any supplemental
indenture or modifying in any manner the rights of the holders of the Notes;
provided, however, that no such supplemental indenture shall (i) extend the
fixed maturity of any Note, or reduce the rate or extend the time of payment of
interest thereon, or reduce the principal amount thereof or premium, if any,
thereon, or reduce any amount payable upon redemption thereof, or impair the
right of any Noteholder to institute suit for the payment thereof, or make the
principal thereof or interest or premium, if any, thereon payable in any coin or
currency other than that provided in the Notes, or modify the provisions of the
Indenture with respect to the subordination of the Notes in a manner adverse to
the Noteholders in any material respect, or change the obligation of the Company
to redeem any Note upon the happening of a Fundamental Change (as defined in the
Indenture) in a manner adverse to the holder of the Notes, or impair the right
to convert the Notes into Common Stock subject to the terms set forth in the
Indenture, including Section 15.6 thereof, without the consent of the holder of
each Note so affected or (ii) reduce the aforesaid percentage of Notes, the
holders of which are required to consent to any such supplemental indenture,
without the consent of the holders of all Notes then outstanding. Subject to the
provisions of the Indenture, the holders of a majority in aggregate principal
amount of the Notes at the time outstanding may on behalf of the holders of all
of the Notes waive any past default or Event of Default under the Indenture and
its consequences except a default in the payment of interest (including
Liquidated Damages, if any) or any premium on, or the principal of, any of the
Notes, or a failure by the Company to convert any Notes into Common Stock of the
Company, or

                                       4
<PAGE>   7
a default in the payment of the redemption price pursuant to Article Three of
the Indenture, or a default in respect of a covenant or provisions of the
Indenture which under Article Eleven of the Indenture cannot be modified without
the consent of the holders of each or all Notes then outstanding or affected
thereby. Any such consent or waiver by the holder of this Note (unless revoked
as provided in the Indenture) shall be conclusive and binding upon such holder
and upon all future holders and owners of this Note and any Notes which may be
issued in exchange or substitution hereof, irrespective of whether or not any
notation thereof is made upon this Note or such other Notes.

         The indebtedness evidenced by the Notes is, to the extent and in the
manner provided in the Indenture, expressly subordinated and subject in right of
payment to the prior payment in full of all Senior Indebtedness of the Company,
whether outstanding at the date of the Indenture or thereafter incurred, and
this Note is issued subject to the provisions of the Indenture with respect to
such subordination. Each holder of this Note, by accepting the same, agrees to
and shall be bound by such provisions and authorizes the Trustee on its behalf
to take such action as may be necessary or appropriate to effectuate the
subordination so provided and appoints the Trustee his attorney-in-fact for such
purpose.

         No reference herein to the Indenture and no provision of this Note or
of the Indenture shall alter or impair the obligation of the Company, which is
absolute and unconditional, to pay the principal of and any premium and interest
(including Liquidated Damages, if any) on this Note at the place, at the
respective times, at the rate and in the coin or currency herein prescribed.

         Interest on the Notes shall be computed on the basis of a 360-day year
of twelve 30-day months.

         The Notes are issuable in fully registered form, without coupons, in
denominations of $1,000 principal amount and any integral multiple of $1,000. At
the office or agency of the Company referred to on the face hereof, and in the
manner and subject to the limitations provided in the Indenture, without payment
of any service charge but with payment of a sum sufficient to cover any tax,
assessment or other governmental charge that may be imposed in connection with
any registration or exchange of Notes, Notes may be exchanged for a like
aggregate principal amount of Notes of any other authorized denominations.

         The Notes may be provisionally redeemed by the Company, in whole or in
part, at any time prior to March 6, 2003, at a redemption price equal to $1,000
per aggregate principal amount of notes to be redeemed plus accrued and unpaid
interest, if any (including Liquidated Damages Amount, if any) to the date of
redemption if (i) the closing price of the Common Stock shall have exceeded 150%
of the conversion price then in effect for at least 20 trading days in any
consecutive 30-trading day period and (ii) if the redemption would occur before
March 1, 2002, the shelf registration statement covering resales of the Notes
and the Common Stock, issuable upon conversion of the Notes, is effective and
available for use and is expected to remain effective and available for use for
the 30 days immediately following the date of


                                       5
<PAGE>   8

         redemption. The Company shall mail notice of any provisional redemption
within five trading days of a consecutive 30-trading day period.

         Upon any such provisional redemption, the Company shall make an
additional Additional Payment (as defined in the Indenture) with respect to the
Notes called for redemption to holders as of the date of mailing of the notice
of provisional redemption in an amount equal to $152.54 per $1,000 Note, minus
the amount of any interest the Company actually paid on such Note prior to the
Notice Date. The Company shall make the Additional Payment on all Notes called
for provisional redemption, including any Notes converted after the date of
mailing of the notice of provisional redemption and prior to the date of
redemption.

         At any time on or after March 6, 2003, and prior to maturity, the Notes
may be redeemed at the option of the Company, in whole or in part, upon mailing
a notice of such redemption not less than 30 days but not more than 60 days
before the date fixed for redemption to the holders of Notes at their last
registered addresses, all as provided in the Indenture, at the following
optional redemption prices (expressed as percentages of the principal amount),
together in each case with accrued and unpaid interest (including Liquidated
Damages, if any) to, but excluding, the date fixed for redemption:

<TABLE>
<CAPTION>

Period                                                                    Redemption Price

<S>                                                                       <C>
Beginning on March 6, 2003 and ending on February 29, 2004                     102.20%

Beginning on March 1, 2004 and ending on February 28, 2005                     110.10%
</TABLE>



and 100% on March 1, 2005; provided, however, that if the date fixed for
redemption is on a March 1 or September 1, then the interest payable on such
date shall be paid to the holder of record on the preceding February 15 or
August 15, respectively.

         The Company may not redeem the Notes if a default in the payment of
interest or premium, if any, on the Notes has occurred and is continuing.

         The Notes are not subject to redemption through the operation of any
sinking fund.


         If a Fundamental Change occurs at any time prior to maturity of the
Notes, the Notes will be redeemable on the 30th day after notice thereof (the
"Repurchase Date") at the option of the holder of the Notes at a redemption
price equal to 100% of the principal amount thereof, together with accrued
interest to (but excluding) the date of redemption; provided, however, that, if
such Repurchase Date is a March 1 or September 1, the interest payable on such
date shall be paid to the holder of record of the Notes on the preceding
February 15 or August 15, respectively. The Notes will be redeemable in
multiples of $1,000 principal amount. The Company shall mail to all holders of
record of the Notes a notice of the occurrence of a Fundamental Change and of
the redemption right arising as a result thereof on or before the 10th day after
the occurrence of such




                                       6
<PAGE>   9
Fundamental Change. For a Note to be so redeemed at the option of the holder,
the Company must receive at the office or agency of the Company maintained for
that purpose in accordance with the terms of the Indenture, such Note with the
form entitled "Option to Elect Repayment Upon a Fundamental Change" on the
reverse thereof duly completed, together with such Note, duly endorsed for
transfer, on or before the 30th day after the date of such notice of a
Fundamental Change (or if such 30th day is not a Business Day, the immediately
succeeding Business Day).


         Subject to the provisions of the Indenture, the holder hereof has the
right, at its option, at any time after the original issuance of any Notes
through the close of business on the final maturity date of the Notes, or, as to
all or any portion hereof called for redemption, prior to the close of business
on the Business Day immediately preceding the date fixed for redemption (unless
the Company shall default in payment due upon redemption thereof), to convert
the principal hereof or any portion of such principal which is $1,000 or an
integral multiple thereof into that number of shares of the Company"s Common
Stock (as such shares shall be constituted at the date of conversion) obtained
by dividing the principal amount of this Note or portion thereof to be converted
by the Conversion Price of $110.18, as may adjusted from time to time as
provided in the Indenture, upon surrender of this Note, together with a
conversion notice as provided in the Indenture (the form entitled "Conversion
Notice" on the reverse hereof), to the Company at the office or agency of the
Company maintained for that purpose in accordance with the terms of the
Indenture, or at the option of such holder, the Corporate Trust Office, and,
unless the shares issuable on conversion are to be issued in the same name as
this Note, duly endorsed by, or accompanied by instruments of transfer in form
satisfactory to the Company duly executed by, the holder or by his duly
authorized attorney. No adjustment in respect of interest on any Note converted
or dividends on any shares issued upon conversion of such Note will be made upon
any conversion except as set forth in the next sentence. If this Note (or
portion hereof) is surrendered for conversion during the period from the close
of business on any record date for the payment of interest to the close of
business on the Business Day preceding the following interest payment date and
either (x) has not been called for redemption on a redemption date that occurs
during such period or (y) is not to be redeemed in connection with a Fundamental
Change on a Repurchase Date that occurs during such period, this Note (or
portion hereof being converted) must be accompanied by an amount, in New York
Clearing House funds or other funds acceptable to the Company, equal to the
interest payable on such interest payment date on the principal amount being
converted; provided, however, that no such payment shall be required if there
shall exist at the time of conversion a default in the payment of interest on
the Notes. No fractional shares will be issued upon any conversion, but an
adjustment and payment in cash will be made, as provided in the Indenture, in
respect of any fraction of a share which would otherwise be issuable upon the
surrender of any Note or Notes for conversion. A Note in respect of which a
holder is exercising its right to require redemption upon a Fundamental Change
may be converted only if such holder withdraws its election to exercise such
right in accordance with the terms of the Indenture. Any Notes called for
redemption, unless surrendered for conversion by the holders thereof on or
before the close of business on the Business Day preceding the date fixed for
redemption, may be deemed to be redeemed from the holders of such Notes for an
amount equal to the applicable redemption price, together with accrued but
unpaid interest



                                       7
<PAGE>   10
(including Liquidated Damages, if any) to (but excluding) the date fixed for
redemption, by one or more investment banks or other purchasers who may agree
with the Company (i) to purchase such Notes from the holders thereof and convert
them into shares of the Company"s Common Stock and (ii) to make payment for such
Notes as aforesaid to the Trustee in trust for the holders.

         Upon due presentment for registration of transfer of this Note at the
office or agency of the Company maintained for that purpose in accordance with
the terms of the Indenture, a new Note or Notes of authorized denominations for
an equal aggregate principal amount will be issued to the transferee in exchange
thereof; subject to the limitations provided in the Indenture, without charge
except for any tax, assessment or other governmental charge imposed in
connection therewith.

         The Company, the Trustee, any authenticating agent, any paying agent,
any conversion agent and any Note registrar may deem and treat the registered
holder hereof as the absolute owner of this Note (whether or not this Note shall
be overdue and notwithstanding any notation of ownership or other writing hereon
made by anyone other than the Company or any Note registrar) for the purpose of
receiving payment hereof, or on account hereof, for the conversion hereof and
for all other purposes, and neither the Company nor the Trustee nor any other
authenticating agent nor any paying agent nor other conversion agent nor any
Note registrar shall be affected by any notice to the contrary. All payments
made to or upon the order of such registered holder shall, to the extent of the
sum or sums paid, satisfy and discharge liability for monies payable on this
Note.

         No recourse for the payment of the principal of or any premium or
interest on this Note, or for any claim based hereon or otherwise in respect
hereof, and no recourse under or upon any obligation, covenant or agreement of
the Company in the Indenture or any supplemental indenture or in any Note, or
because of the creation of any indebtedness represented thereby, shall be had
against any incorporator, stockholder, employee, agent, officer or director or
subsidiary, as such, past, present or future, of the Company or of any successor
corporation, either directly or through the Company or any successor
corporation, whether by virtue of any constitution, statute or rule of law or by
the enforcement of any assessment or penalty or otherwise, all such liability
being, by acceptance hereof and as part of the consideration for the issue
hereof, expressly waived and released.

         This Note shall be deemed to be a contract made under the laws of New
York, and for all purposes shall be construed in accordance with the laws of New
York, without regard to principles of conflicts of laws.

         Terms used in this Note and defined in the Indenture are used herein as
therein defined.



                                       8
<PAGE>   11
                                  ABBREVIATIONS

         The following abbreviations, when used in the inscription of the face
of this Note, shall be construed as though they were written out in full
according to applicable laws or regulations.


--------------------------------------------------------------------------------
TEN COM-  as tenants in common             UNIF GIFT MIN ACT --
                                                  ____________________ Custodian
                                                       (Cust)

                                                  ____________________
                                                       (Minor)
--------------------------------------------------------------------------------
TEN ENT-  as tenants by the entireties
--------------------------------------------------------------------------------
JT TEN-   as joint tenants with right of       under Uniform Gifts to Minors Act
          survivorship and not as tenants in
          common                               ____________________
                                                     (State)

--------------------------------------------------------------------------------
                    ADDITIONAL ABBREVIATIONS MAY ALSO BE USED
                          THOUGH NOT IN THE ABOVE LIST.





                                      A-1
<PAGE>   12
                                CONVERSION NOTICE


TO:      IMCLONE SYSTEMS INCORPORATED
         THE BANK OF NEW YORK

         The undersigned registered owner of this Note hereby irrevocably
exercises the option to convert this Note, or the portion thereof (which is
$1,000 or an integral multiple thereof) below designated, into shares of Common
Stock of ImClone Systems Incorporated in accordance with the terms of the
Indenture referred to in this Note, and directs that the shares issuable and
deliverable upon such conversion, together with any check in payment for
fractional shares and any Notes representing any unconverted principal amount
hereof, be issued and delivered to the registered holder hereof unless a
different name has been indicated below. If shares or any portion of this Note
not converted are to be issued in the name of a person other than the
undersigned, the undersigned will provide the appropriate information below and
pay all transfer taxes payable with respect thereto. Any amount required to be
paid by the undersigned on account of interest accompanies this Note.

Dated: ___________________

                            ___________________________________

                            ___________________________________
                            Signature(s)

                            Signature(s) must be guaranteed by an "eligible
                            guarantor institution" meeting the requirements of
                            the Note registrar, which requirements include
                            membership or participation in the Security Transfer
                            Agent Medallion Program ("STAMP") or such other
                            "signature guarantee program" as may be determined
                            by the Note registrar in addition to, or in
                            substitution for, STAMP, all in accordance with the
                            Securities Exchange Act of 1934, as amended.

                            ___________________________________
                            Signature Guarantee



                                      B-1
<PAGE>   13
         Fill in the registration of shares of Common Stock if to be issued, and
Notes if to be delivered, other than to and in the name of the registered
holder:


----------------------------------------
(Name)

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

----------------------------------------
(City, State and Zip Code)

----------------------------------------
Please print name and address

Principal amount to be converted
(if less than all):

$
 ----------------------------------------

Social Security or Other Taxpayer
Identification Number:

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


                                      B-2
<PAGE>   14
                            OPTION TO ELECT REPAYMENT

                            UPON A FUNDAMENTAL CHANGE


TO:      IMCLONE SYSTEMS INCORPORATED
         THE BANK OF NEW YORK

         The undersigned registered owner of this Note hereby irrevocably
acknowledges receipt of a notice from ImClone Systems Incorporated (the
"Company") as to the occurrence of a Fundamental Change with respect to the
Company and requests and instructs the Company to repay the entire principal
amount of this Note, or the portion thereof (which is $1,000 or an integral
multiple thereof) below designated, in accordance with the terms of the
Indenture referred to in this Note at the price of 100% of such entire principal
amount or portion thereof, together with accrued interest to, but excluding,
such repayment date, to the registered holder hereof.

Dated: ___________________


                             ___________________________________

                             ___________________________________
                                    Signature(s)

                            NOTICE: The above signatures of the holder(s) hereof
                            must correspond with the name as written upon the
                            face of the Note in every particular without
                            alteration or enlargement or any change whatever.

                            Principal amount to be repaid (if less than all):


                            $ _____________________________

                            _______________________________
                            Social Security or Other
                            Taxpayer Identification Number



                                       C-1
<PAGE>   15
                                   ASSIGNMENT

For value received __________________________________________ hereby sell(s)
assign(s) and transfer(s) unto ____________________________________ (Please
insert social security or other Taxpayer Identification Number of assignee) the
within Note, and hereby irrevocably constitutes and appoints
____________________________________ attorney to transfer said Note on the books
of the Company, with full power of substitution in the premises.

         In connection with any transfer of the Note prior to the expiration of
the holding period applicable to sales thereof under Rule 144(k) under the
Securities Act (or any successor provision) (other than any transfer pursuant to
a registration statement that has been declared effective under the Securities
Act), the undersigned confirms that such Note is being transferred:

         / /      To ImClone Systems Incorporated or a subsidiary thereof; or

         / /      Inside the United States pursuant to and in compliance with
                  Rule 144A under the Securities Act of 1933, as amended; or

         / /      Inside the United States to an Institutional Accredited
                  Investor pursuant to and in compliance with the Securities Act
                  of 1933, as amended, in a minimum denomination of $100,000; or

         / /      Outside the United States in compliance with Rule 904 under
                  the Securities Act; or

         / /      Pursuant to and in compliance with Rule 144 under the
                  Securities Act of 1933, as amended;

and unless the box below is checked, the undersigned confirms that such Note is
not being transferred to an "affiliate" of the Company as defined in Rule 144
under the Securities Act of 1933, as amended (an "Affiliate").

         / /      The transferee is an Affiliate of the Company.

Dated: ___________________





                                      D-1
<PAGE>   16
                            ___________________________________


                            ___________________________________
                            Signature(s)

                            Signature(s) must be guaranteed by an "eligible
                            guarantor institution" meeting the requirements of
                            the Note registrar, which requirements include
                            membership or participation in the Security Transfer
                            Agent Medallion Program ("STAMP") or such other
                            "signature guarantee program" as may be determined
                            by the Note registrar in addition to, or in
                            substitution for, STAMP, all in accordance with the
                            Securities Exchange Act of 1934, as amended.

                            ___________________________________
                            Signature Guarantee

NOTICE: The signature of the conversion notice, the option to elect repayment
upon a Fundamental Change or the assignment must correspond with the name as
written upon the face of the Note in every particular without alteration or
enlargement or any change whatever.


                                      D-2