<PAGE>

                                                                   Exhibit 10.23


                                   AGREEMENT
                                   ---------

          This Agreement (the "Agreement") is made as of the 31st day of
December, 1997 by and between VIMRx Pharmaceuticals Inc., a Delaware corporation
with offices at 2751 Centerville Road, Wilmington, Delaware 19808 ("VIMRx"), and
Innovir Laboratories, Inc., a Delaware corporation with offices at 510 East 73rd
Street, New York, New York 10021 ("Innovir").

                                R E C I T A L S
                                - - - - - - - -

          WHEREAS, Innovir has requested that VIMRx make an equity investment in
Innovir of $2,000,000 at this time and, based upon the cash requirements of
Innovir, up to an additional $5,000,000 during the next two years; and

          WHEREAS, VIMRx is willing to make such equity investments upon the
terms and conditions set forth herein.

          NOW, THEREFORE, Innovir and VIMRx hereby agree as follows:

          1.   Purchase of Common Stock and Issuance of Warrants.
               -------------------------------------------------

          (a)  Initial Purchase of Common Stock.  Simultaneously with the
               --------------------------------
execution and delivery hereof, VIMRx shall pay $2,000,000 to Innovir as the
aggregate purchase price for, and Innovir shall cause the issuance to VIMRx of,
5,080,436 shares of the common stock, $.013 par value per share (the "Common
Stock"), of Innovir.

          (b)  Subsequent Purchases of Common Stock.  During the two-year period
               ------------------------------------
commencing on the date hereof, Innovir shall have the right to deliver
periodically to VIMRx a notice stating the amount of cash reasonably required by
Innovir from VIMRx.  Within fifteen days after its receipt of each such notice,
VIMRx shall pay such amount to Innovir and Innovir shall thereafter promptly
cause the issuance to VIMRx of such number of shares of Common Stock as shall
equal the quotient of the amount then paid by VIMRX to Innovir divided by the
lower of (i) the average closing bid price per share of the Common Stock for the
fifteen trading days immediately preceding the date such notice is given and
(ii) $1.30; provided, however, that in no event shall VIMRx be required to pay
            --------  -------
Innovir more than $5,000,000 in the aggregate pursuant to this Section 1(b); and

provided, further, that VIMRx shall no longer be required to pay Innovir any
--------  -------
amounts pursuant to this Section 1(b) in the event that VIMRx ceases to own at
least fifty percent of the outstanding shares of Common Stock.

          (c)  Issuance of Warrants.  Simultaneously with the execution and
               --------------------
delivery hereof, Innovir shall execute and deliver to VIMRx a warrant to
purchase 1,000,000 shares of Common Stock at $.393667 per share (the "Warrant"),
in the form of the warrant attached hereto as Exhibit A.
<PAGE>

          2.   Representations.
               ---------------

               (a)  Representations of Innovir.  Innovir hereby represents and
                    --------------------------
warrants to VIMRx as follows:

                    (i)   This Agreement has been duly authorized, executed and
delivered by Innovir and constitutes the valid and legally binding agreement of
Innovir, enforceable against Innovir in accordance with its terms.

                    (ii)  The shares of Common Stock to be issued pursuant to
Sections 1(a) and 1(b), when issued and delivered in accordance with the terms
of this Agreement, will be validly issued, fully paid and non-assessable.

                    (iii) The Warrant has been duly authorized, executed and
delivered by Innovir and constitutes the valid and legally binding obligation of
Innovir, enforceable against Innovir in accordance with its terms.  The shares
of Common Stock issuable upon exercise thereof will be duly reserved for
issuance and, when issued upon such exercise, will be validly issued, fully paid
and non-assessable.

               (b)  Representations of VIMRX.  VIMRx hereby represents and
                    ------------------------
warrants to Innovir as follows:

                    (i)   This Agreement has been duly authorized, executed and
delivered by VIMRX and constitutes the valid and legally binding agreement of
VIMRx, enforceable against VIMRx in accordance with its terms.

                    (ii)  VIMRx is acquiring hereunder the shares of Common
Stock and the Warrant for its own account for investment within the
contemplation of the Securities Act of 1933, as amended, and not with a view to
the transfer or resale thereof.

          3.   Miscellaneous.
               -------------

               (a)  Modification; Waiver.  This Agreement may be amended,
                    --------------------
modified and supplemented only by a writing signed by both Innovir and VIMRx.
Any failure of Innovir or VIMRx to comply with any obligation, covenant,
agreement or condition herein contained may be expressly waived, in writing
only, by (i) Innovir in the case of any failure of VIMRx or (ii) VIMRx in the
case of any failure of Innovir. Such waiver shall be effective only in the
specific instance and for the specific purpose for which made or given.

               (b)  Notices.  All notices, requests, demands and other
                    -------
communications required or permitted hereunder shall be made in writing, and
shall be duly given when received by the receiving party by hand, mail or
facsimile, as follows:

                                       2
<PAGE>

                    If to Innovir:

                    Innovir Laboratories, Inc.
                    510 East 73rd Street
                    New York, New York  10021
                    Fax # (212) 249-4513
                    Attn:  Frank O'Connell

                    With a copy to:

                    Fulbright & Jaworski L.L.P.
                    666 Fifth Avenue
                    New York, New York 10103
                    Fax # (212) 752-5958
                    Attn:  Merrill M. Kraines, Esq.

or to such other person or place as Innovir shall designate by notice in the
manner provided in this Section 3(b);

                    If to VIMRx:

                    VIMRX Pharmaceuticals Inc.
                    2751 Centerville Road
                    Wilmington, Delaware 19808
                    Fax # (302) 998-3794
                    Attn:  Bill McIntosh

                    With a copy to:

                    Epstein Becker & Green, P.C.
                    250 Park Avenue
                    New York, New York  10177
                    Fax # (212) 661-0989
                    Attn:  Lowell S. Lifschultz, Esq.

or to such other person or place as VIMRx shall designate by notice in the
manner provided in this Section 3(b).

          (c)  Assignment.  This Agreement shall be binding upon and inure to
               ----------
the benefit of Innovir and its successors and assigns, and to VIMRx and its
successors and assigns, but neither this Agreement nor any of the rights,
interests and obligations hereunder shall be assigned or delegated by either of
Innovir or VIMRx without the prior written consent of the other and any
purported assignment or delegation in violation hereof shall be null and void ab
initio.

                                       3
<PAGE>

          (d)  Governing Law.  This Agreement shall be governed by and construed
               -------------
solely in accordance with the laws of the State of Delaware, without regard to
principles of conflicts of laws.

          (e)  Counterparts.  This Agreement may be executed in two or more
               ------------
counterparts, each of which shall be deemed an original, but all of which taken
together shall constitute one and the same instrument.

          (f)  Entire Agreement.  This Agreement contains the entire
               ----------------
understanding of the parties in respect of the subject matter contained herein
and there are no other terms or conditions, representations or warranties,
written or oral, express or implied, except as expressly set forth herein.

          IN WITNESS WHEREOF, the parties have caused this Agreement to be duly
executed as of the day and year first above written.

                                        INNOVIR LABORATORIES, INC.


                                        By: /s/ Thomas Sharpe
                                            ---------------------------
                                           Name:  Thomas Sharpe
                                           Title: President

                                        VIMRx PHARMACEUTICALS INC.


                                        By: /s/ Richard L. Dunning
                                            ---------------------------
                                           Name:   Richard L. Dunning
                                           Title:  President

                                       4
<PAGE>

                                                                       EXHIBIT A
                                                                       ---------

                                FORM OF WARRANT
                                ---------------


See attached form of Warrant.
<PAGE>

THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAWS AND NEITHER THE SECURITIES
NOR ANY INTEREST THEREIN MAY BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR OTHERWISE
DISPOSED OF EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH
ACT OR SUCH LAWS OR AN EXEMPTION FROM REGISTRATION UNDER SUCH ACT AND SUCH LAWS,
WHICH, IN THE OPINION OF COUNSEL FOR THE HOLDER, WHICH COUNSEL AND OPINION ARE
REASONABLY SATISFACTORY TO COUNSEL FOR THIS CORPORATION, IS AVAILABLE.


                  WARRANT TO PURCHASE SHARES OF COMMON STOCK
                         OF INNOVIR LABORATORIES, INC.


Warrant Certificate No. V-3                                    December 31, 1997


     This certifies that, for value received, Innovir Laboratories, Inc., a
Delaware corporation (the "COMPANY"), hereby grants to VIMRx Pharmaceuticals
Inc. (the "HOLDER") the right to purchase, subject to adjustment and the other
terms and conditions set forth herein, One Million (1,000,000) fully paid and
nonassessable shares of the Company's common stock, $.013 par value per share
(the "STOCK"), at a price per share, subject to adjustment as set forth below,
of $.393667 (the "WARRANT EXERCISE PRICE") at any time or from time to time
after the date hereof and prior to 5:00 P.M. (Eastern Time) on December 31, 2002
(the "WARRANT EXPIRATION DATE").  This Warrant and all warrants hereafter issued
in exchange or substitution of this Warrant, are hereinafter referred to as the
"WARRANTS."  THIS WARRANT, TO THE EXTENT NOT EXERCISED IN THE MANNER SET FORTH
HEREIN, SHALL TERMINATE AND BECOME NULL AND VOID AT 5:00 P.M. (EASTERN TIME) ON
THE WARRANT EXPIRATION DATE.

     This Warrant is subject to the following terms and conditions.

     1.   Exercise; Issuance of Certificates; Payment of Shares.
          -----------------------------------------------------

          (a)  This Warrant may be exercised, at the option of the Holder, in
whole or in part at any time prior to 5:00 P.M. (Eastern Time) on the Warrant
Expiration Date, by surrender to the Company of this Warrant Certificate
properly endorsed together with the Form of Subscription attached hereto duly
completed, signed and with proper payment of the Warrant Exercise Price
multiplied by the number of shares of Stock for which the Warrant is being
exercised.  Payment shall be in cash, certified check or official bank check,
payable to the order of the Company.

          (b)  The Company agrees that the shares of Stock purchased on the
exercise of each Warrant shall be deemed to be issued as of the close of
business on the date on which this Warrant Certificate shall have been
surrendered and payment made for such shares of Stock.  Issuance of the shares
of Stock shall be subject to compliance with all provisions of the Securities
Act of 1933, as amended (the "SECURITIES ACT"), the Securities Exchange Act of
1934, as amended (the "EXCHANGE ACT"), and any relevant state securities
law.  Subject to the provisions of Section 2 hereof, certificates for the
<PAGE>

largest whole number of shares of Stock so purchased, together with any other
securities or property to which the Holder is entitled upon such exercise, shall
be delivered to the Holder by the Company within a reasonable time after this
Warrant has been exercised.  No fractional shares of Stock shall be issued upon
exercise of this Warrant.  Each stock certificate so delivered shall be
registered in the name of the Holder or such other name as shall be designated
by the Holder, subject to the provisions of Sections 6 and 8 hereof.  If prior
to the Warrant Expiration Date, this Warrant is exercised in part, one or more
new Warrants substantially in the form of, and on the terms contained in, this
Warrant Certificate will be issued for the remaining number of shares of Stock
in respect of which this Warrant has not been exercised.

     2.   Shares to be Fully Paid; Reservation of Shares.  The Company covenants
          ----------------------------------------------
and agrees that all shares of Stock which may be issued upon the exercise of
this Warrant will, upon issuance, be duly authorized, validly issued, fully paid
and nonassessable.  The Company further covenants and agrees that during the
period within which this Warrant may be exercised, the Company will at all times
have authorized and reserved, and will keep available solely for issuance upon
exercise of this Warrant, a sufficient number of shares of Stock or other
securities and properties as from time to time shall be receivable upon the
exercise of this Warrant.  The Company shall provide that any successor
corporation will reserve a sufficient number of shares of authorized but
unissued stock or other securities or set aside sufficient other property, as
the case may be, as provided for in this Section 2.

     3.   Adjustment of Warrant Exercise Price and Number of Shares; Events
          -----------------------------------------------------------------
Requiring Notice; Changes in Stock.
----------------------------------

          3.1  Method of Adjustment.  The Warrant Exercise Price and the number
               --------------------
of shares of Stock purchasable upon the exercise of this Warrant shall be
subject to adjustment from time to time upon the occurrence of the events
described in Section 3.2.  Upon each adjustment of the Warrant Exercise Price,
the Holder shall thereafter be entitled to purchase, at the Warrant Exercise
Price resulting from such adjustment, the number of shares of Stock obtained by
multiplying the Warrant Exercise price in effect immediately prior to such
adjustment by the number of shares of Stock purchasable pursuant hereto
immediately prior to such adjustment, and dividing the product thereof by the
Warrant Exercise Price resulting from such adjustment.

          3.2  Events Requiring Adjustment of Warrant Exercise Price.
               -----------------------------------------------------

               (a)  In case the Company shall at any time subdivide its
outstanding shares of Stock into a greater number of shares of Stock or declare
a dividend upon its Stock payable solely in shares of Stock, the Warrant
Exercise Price in effect immediately prior to such subdivision or dividend shall
be proportionately reduced, and conversely, in case the outstanding shares of
Stock of the Company shall be combined into a smaller number of shares of Stock,
the Warrant Exercise Price in effect immediately prior to such combination shall
be proportionately increased.

               (b)  Except as provided in subsection (a) above, and except for

                                      -2-
<PAGE>

any issuances of Stock pursuant to the Agreement of even date herewith between
the Company and the Holder, Warrant No. V-2 previously issued by the Company to
the Holder, or this Warrant, in the event the Company shall hereafter issue or
sell any Stock at a price per share, or any securities convertible into Stock or
any rights, options or warrants to purchase Stock or securities convertible into
Stock, or entitling the holders thereof to purchase Stock, at a price per share
(determined by dividing (i) the total amount, if any, received or receivable by
the Company in consideration of the issuance or sale of such securities plus the
consideration, if any, payable to the Company upon exercise or conversion
thereof (collectively, the "TOTAL CONSIDERATION") by (ii) the number of
additional shares of Stock issued, sold or issuable upon exercise or conversion
of such securities), which is less than the lower of the then fair market value
of the Stock or the Warrant Exercise Price, the Warrant Exercise Price shall be
adjusted as of the date of such issuance or sale by multiplying the Warrant
Exercise Price then in effect by a fraction, the numerator of which shall be (x)
the sum of (A) the number of shares of Stock outstanding on the record date of
such issuance or sale plus (B) the Total Consideration divided by the then fair
market value of the Stock and the denominator of which shall be (y) the number
of shares of Stock outstanding on the record date of such issuance or sale plus
the maximum number of additional shares of Stock issued, sold or issuable upon
exercise or conversion of such securities.

          3.3  Notice of Adjustment.  Upon any adjustment of the Warrant
               --------------------
Exercise Price and any increase or decrease in the number of shares of Stock
purchasable upon the exercise of this Warrant, the Company promptly shall give
written notice thereof to the Holder, which shall state the Warrant Exercise
Price resulting from such adjustment and increase or decrease, if any, in the
number of shares of Stock purchasable at such price upon the exercise of this
Warrant, setting forth in reasonable detail the method of calculation and the
facts upon which such calculation is based.

          3.4  Other Notices.  If at any time:
               -------------

               (a)  the Company shall declare any cash dividend upon its Stock;

               (b)  the Company shall declare any dividend upon its Stock
payable in stock (other than a dividend payable solely in shares of Stock) or
make any special dividend or other distribution to the holders of its Stock;

               (c)  there shall be any consolidation or merger of the Company
with another corporation, or a sale of all or substantially all of the Company's
assets to another corporation; or

               (d)  there shall be a voluntary or involuntary dissolution,
liquidation or winding-up of the Company;

then, in any one or more of said cases, the Company shall give the Holder (i) at
least twelve (12) calendar days' prior written notice of the date on which the
books of the Company shall close or a record date shall occur for such dividend
or distribution or for determining rights to vote in respect of any such
consolidation, merger, sale,

                                      -3-
<PAGE>

dissolution, liquidation or winding-up, and (ii) in the case of any such
consolidation, merger, sale, dissolution, liquidation or winding-up, at least
twelve (12) calendar days' prior written notice of the date when the same shall
take place. Any notice given in accordance with clause (i) above shall also
specify, in the case of any such dividend or distribution, the date on which the
holders of Stock shall be entitled thereof. Any notice given in accordance with
clause (ii) above shall also specify the date on which the holders of Stock
shall be entitled to exchange their Stock for securities or other property
deliverable upon such consolidation, merger, sale, dissolution, liquidation or
winding-up, as the case may be. Notwithstanding anything contained herein to the
contrary, if the Holder does not exercise this Warrant prior to a record date or
the occurrence of an event described above, as applicable, except as provided in
Section 3.2, the Holder shall not be entitled to receive the benefits accruing
to existing holders of the Stock in such event.

     4.   Issue Tax.  The issuance of certificates for shares of Stock upon the
          ---------
exercise of this Warrant shall be made without charge to the Holder for any
issue tax in respect thereof; provided, however, that the Company shall not be
required to pay any tax which may be payable in respect of any transfer involved
in the issuance and delivery of any certificate in a name other than that of the
Holder.

     5.   No Voting or Dividend Rights.  This Warrant does not confer upon the
          ----------------------------
Holder the right to vote or to consent or to receive notice as a stockholder of
the Company, in respect of meetings of stockholders for the election of
directors of the Company or any other matters or any rights whatsoever as a
stockholder of the Company prior to the exercise hereof.  No cash dividends
shall be payable or accrued in respect of this Warrant or the shares of Stock
purchasable hereunder until, and only to the extent that, this Warrant shall
have been exercised.

     6.   Restrictions on Transferability of Securities; Compliance with
          --------------------------------------------------------------
Securities Act.
--------------

          6.1  Restrictions on Transferability.  In no event shall the Company
               -------------------------------
be obligated to effect any transfer of this Warrant unless a registration
statement is in effect with respect thereto under applicable state and Federal
securities laws or the Company has received an opinion in substance reasonably
satisfactory to it from counsel reasonably satisfactory to it that such
registration is not required and this Warrant is surrendered to the Company at
its principal office together with the Assignment Form annexed hereto, duly
completed and executed, and sufficient funds to pay any transfer tax.

               Shares of Stock purchased upon the exercise of this Warrant shall
only be transferred by the Company in accordance with the Securities Act.

          6.2  Ownership.  The Company and any agent of the Company may treat
               ---------
the person in whose name this Warrant Certificate is registered on the register
which the Company shall cause to be maintained for such purpose as the owner and
holder thereof for all purposes.  This Warrant Certificate, if properly
assigned, may be exercised by a new holder without first having a new Warrant
Certificate issued.

     7.   Modification and Waiver.  This Warrant and any provision hereof may be
          -----------------------
changed, waived, discharged or terminated only by an instrument in writing
signed by the

                                      -4-
<PAGE>

party against which enforcement of the same is sought.

     8.   Notices.  Any notice, request or other document required or permitted
          -------
to be given or delivered to the Holder or the Company shall be personally
delivered or shall be sent by certified or registered mail, postage prepaid, if
to the Holder at its address as shown on the books of the Company, or if to the
Company at its principal office at 510 East 73rd Street, New York, New York
10021, Attention: Vice President-Finance.  Any notice, request or other document
shall be deemed to have been given upon receipt if personally delivered, or on
the fifth day after being mailed if mailed, registered or certified mail.  The
Company shall notify the Holder in writing of any change of address of the
Company within a reasonable time following such change of address.

     9.   Descriptive Headings and Governing Law.  The descriptive headings of
          --------------------------------------
the several sections and paragraphs of this Warrant Certificate are inserted for
convenience only and do not constitute a part of this Warrant Certificate.  This
Warrant Certificate shall be construed and enforced in accordance with, and the
rights of the parties shall be governed by, the laws of the State of Delaware.

     10.  Lost Warrant Certificates or Stock Certificates.  Upon receipt of
          -----------------------------------------------
evidence reasonably satisfactory to the Company of the loss, theft, destruction,
or mutilation of this Warrant Certificate or any stock certificate deliverable
upon the exercise hereof and, in the case of any such loss, theft or
destruction, upon receipt of an indemnity and, if requested, bond reasonably
satisfactory to the Company, or in the case of any such mutilation upon
surrender and cancellation of this Warrant Certificate or such stock
certificate, the Company at its expense shall make and deliver a new Warrant
Certificate or stock certificate, of like tenor, in lieu of the lost, stolen,
destroyed or mutilated Warrant Certificate or stock certificate.

     IN WITNESS WHEREOF, the Company has caused this Warrant Certificate to be
executed by its duly authorized officer as of the 31st day of December, 1997.

                                        INNOVIR LABORATORIES, INC.


                                        By: /s/  Thomas Sharpe, Ph.D.
                                            -----------------------------
                                            Name:  Thomas Sharpe, Ph.D.
                                            Title: President

ATTEST:


By: /s/ Francis M.O'Connell
   -----------------------------
Name:  Francis M. O'Connell
Title: Chief Financial Officer

                                      -5-
<PAGE>

                             FORM OF SUBSCRIPTION

                  (To be signed only on exercise of Warrant)


TO: INNOVIR LABORATORIES, INC.

          The undersigned, the holder of the within Warrant, hereby irrevocably
elects to exercise this Warrant for, and to purchase thereunder, _______________
shares of Common Stock of INNOVIR LABORATORIES, INC. and herewith makes payment
of $____________ therefor and requests that the certificates for such shares be
issued in the name of, and delivered to, _______________________________, whose
address is ___________________________________________.


Dated:  ______________, _____

                                   ___________________________________
                                   (Signature must conform to name of
                                   Holder as specified on the face of
                                   the Warrant)


                                   ___________________________________

                                   ___________________________________
                                                  (Address)

                                      -6-
<PAGE>

                              FORM OF ASSIGNMENT

            (To be signed only on transfer of Warrant in accordance
         with the provisions of Section 6 of the Warrant Certificate)


          For value received, the undersigned hereby sells, assigns, and
transfers unto _____________________ the right represented by the written
Warrant to purchase shares of Common Stock of INNOVIR LABORATORIES, INC. to
which the within Warrant relates and appoints _____________________ Attorney to
transfer such rights on the books of INNOVIR LABORATORIES, INC. with full power
of substitution in the premises.


Dated:  _____________, _____


                                   ___________________________________
                                   (Signature must conform to name of
                                   Holder as specified on the face of
                                   the Warrant)

                                      -7-