Exhibit 4.23

THIS NOTE HAS BEEN ACQUIRED FOR INVESTMENT PURPOSES ONLY AND MAY NOT BE SOLD,
TRANSFERRED OR OTHERWISE DISPOSED OF UNTIL (I) A REGISTRATION STATEMENT UNDER
THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), SHALL HAVE BECOME EFFECTIVE
WITH RESPECT THERETO OR (II) RECEIPT BY THE COMPANY OF AN OPINION OF COUNSEL
REASONABLY SATISFACTORY TO THE COMPANY TO THE EFFECT THAT REGISTRATION UNDER THE
ACT IS NOT REQUIRED IN CONNECTION WITH SUCH PROPOSED TRANSFER NOR IS IN
VIOLATION OF ANY APPLICABLE STATE SECURITIES LAWS. THIS LEGEND SHALL BE ENDORSED
UPON ANY NOTE ISSUED IN EXCHANGE FOR THIS NOTE.

THIS NOTE IS SUBJECT TO THE TERMS OF A PURCHASE AGREEMENT, DATED AS OF JANUARY
31, 2000, AS AMENDED BY AN AGREEMENT DATED AS OF MARCH 16, 2001, COPIES OF WHICH
ARE ON FILE AT THE EXECUTIVE OFFICES OF MILESTONE SCIENTIFIC INC.

                            MILESTONE SCIENTIFIC INC.
                         SENIOR SECURED PROMISSORY NOTE

$14,495.69                                                        March 16, 2001
                                                          Livingston, New Jersey

      FOR VALUE RECEIVED, MILESTONE SCIENTIFIC INC., a Delaware corporation (the
"Company" or "Maker") with its principal executive office at 220 South Orange
Avenue, Livingston, New Jersey 07039, promises to pay to

                     LONGVIEW PARTNERS LP c/o Cumberland
                     Associates LLC 1114 Avenue of the Americas
                     New York, New York 10036

(the "Payee" or the "holder of this Note"), or registered assigns, the face
amount (which includes interest to maturity at the rate of 20% per year) of

      FOURTEEN THOUSAND FOUR HUNDRED NINETY FIVE and 69/100 DOLLARS
($14,495.69), 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, or such other form as shall be acceptable by the Payee in its sole and
absolute discretion together with interest as set forth in Section 1 of this
Note at such times and in such amounts as set forth in Section 2 of this Note,
at Payee's address designated above or at such other place as the Payee shall
have notified the Company in writing at least five (5) days before such payment
is due.

      This Note is one of a series of similar notes (collectively referred to as
the "Notes") issued pursuant to a Purchase Agreement between the Company and
Payee, dated as of January 31, 2000 (the "Agreement"), as amended on March 16,
2001 (the Amendment"), copies of which are available for inspection at the
Company's principal office. This Note is entitled to the benefit of certain
terms, conditions, covenants and agreements contained in the Agreement. Unless
otherwise specifically provided herein to the contrary, capitalized terms used
herein shall have the same meaning ascribed to such terms in the Agreement.

<PAGE>

      1. Interest.

            A. If an Event of Default (as defined in the Agreement) shall have
occurred and shall continue while this Note is outstanding, interest on the
unpaid principal balance of this Note shall accrue at a rate equal to the
maximum rate permitted by law (such rate is hereinafter referred to as the
"Default Rate").

            B. In the event a registration statement covering any shares of the
Company's Common Stock (as defined below) that may be issued as payment of the
face amount due on this Note or on exercise of certain warrants issued on
January 31, 2000 (collectively, the "Registerable Securities") is not effective
on or before July 15, 2000, in accordance with the terms of a Registration
Rights Agreement between the Company and the Payee, dated even date herewith,
interest on the principal amount hereof shall accrue at the rate of 16% per
annum from such date until the earlier of (x) the effective date of a
registration statement covering the Registerable Securities or (y) the date on
which the Registerable Securities are salable pursuant to Rule 144 promulgated
under the Securities Act of 1933, as amended, during a period of not more than
90 days.

            C. Interest as aforesaid shall be calculated on the basis of actual
number of days elapsed over a year of 360 days.

      2. Payment of Face Amount.

            A. The entire face amount of this Note shall be due and payable on
the Maturity Date (as defined below).

            B. At the option of the Company, the face amount of this Note shall
be payable either in cash or in shares of the Company's Common Stock. Par value
$.001 per share (the "Common Stock"), valued at the average closing price per
share of the Common Stock for the five trading days ending the day prior to the
Maturity Date of the New Notes, provided that such shares of Common Stock have
been registered pursuant to the Registration Rights Agreement between the
Company and Payee, dated January 31, 2000.

            C. The Company shall pay to Payee 108% of the face amount of this
Note if there is a change in control of the Company prior to the Maturity Date.
For the purposes of this provision, a "change in control of the Company" shall
be deemed to occur if: (1) there shall be consummated (a) any consolidation or
merger of the Company in which the Company is not the continuing or surviving
corporation or pursuant to which shares of the Company's Common Stock would be
converted into cash, securities or other property, other than a merger of the
Company in which the holders of the Common Stock immediately prior to the merger
have not less than 50% of the ownership of common stock of the surviving
corporation immediately after the merger, or (b) any sale, lease, exchange or
other transfer (in one transaction or a series of related transactions) of all,
or substantially all, of the assets of the Company; or (2) the stockholders of
the Company shall approve any plan or proposal for liquidation or dissolution of
the Company; or (3) any person (as such term is used in Section 13(d) and
14(d)(2) of the Securities Exchange Act of 1934, as amended (the "Exchange
Act")) who, at the time of the


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<PAGE>

execution of this Agreement, does not own 5% or more of the Company's
outstanding Common Stock, shall become the beneficial owner (within the meaning
of Rule 13d-3 under the Exchange Act) of 40% or more of the outstanding Common
Stock other than pursuant to a plan or arrangement entered into by such person
and the Company; or (4) during any period of two consecutive years commencing on
the date hereof, individuals who at the beginning of such period constitute the
entire Board of Directors shall cease for any reason to constitute a majority
thereof unless the election, or the nomination for election by the Company's
stockholders, of each new director was approved by a vote of at least two-thirds
of the directors then still in office who were directors at the beginning of the
period.

      3. Maturity. This Note shall mature, and the entire unpaid face amount
hereof shall be due in full on March 31, 2002 (the "Maturity Date").

      4. Security. This Note is a secured by raw material, work in process and
finished goods inventories and certain proceeds thereof of the Company pursuant
to a Security Agreement dated even date herewith.

      5. Priority. The payment of the entire face amount of this Note shall be
senior in right of payment to all other indebtedness of the Company whether
incurred prior or subsequent to the date hereof other than (i) any purchase
money obligations incurred by the Company in connection with the purchase of
property in the ordinary course of business, (ii) all payment obligations of the
Company pursuant to any capitalized lease entered into by the Company, and (iii)
all payables incurred by the Company in the ordinary course of its business.

      6. Events of Default and Remedies.

            A. Events of Default. Each of the following events is herein
referred to as an Event of Default:

                  (i) if any representation or warranty made herein, or in the
Agreement, or in any report, certificate, financial statement or other
instrument furnished in connection with this Note or the Agreement, shall be
false, inaccurate or misleading in any material respect when made or when deemed
made hereunder;

                  (ii) any default in the payment of the face amount hereof when
the same shall be due and payable, whether at the due date thereof or by
acceleration or otherwise;

                  (iii) any material default in the due observance or
performance of any other covenant, condition or agreement to be observed or
performed pursuant to the terms hereof or the Agreement, and the continuance of
such default unremedied for a period of twenty (20) days after written notice
thereof to the Company setting forth in reasonable detail the circumstances of
such Event of Default;

                  (iv) if the Company shall: (A) apply for or consent to the
appointment of a receiver, trustee, custodian or liquidator of it or any of its
properties, (B) admit in writing its inability to pay its debts as they mature,
(C) make a general assignment for the benefit of


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<PAGE>

creditors, (D) be adjudicated a bankrupt or insolvent or be the subject of an
order for relief under Title 11 of the United States Code, or (E) file a
voluntary petition in bankruptcy, or a petition or an answer seeking
reorganization or an arrangement with creditors or to take advantage or any
bankruptcy, reorganization, insolvency, readjustment of debt, dissolution or
liquidation law or statute, or an answer admitting the material allegations of a
petition filed against him or it in any proceeding under any such law, or (vi)
take or permit to be taken any action in furtherance of or for the purpose of
effecting any of the foregoing;

                  (v) if any order, judgment or decree shall be entered, without
the application, approval or consent of the Company, by any court of competent
jurisdiction, approving a petition seeking reorganization of the Company, or
appointing a receiver, trustee, custodian or liquidator of any of the Company,
or of all or any substantial part of its assets, and such order, judgment or
decree shall continue unstayed and in effect for any period of sixty (60)
consecutive days;

                  (vi) there shall be a default (taking into account lapse of
notice, written notice to the Company or both) under any bond, debenture, note
or other evidence of indebtedness for money borrowed or under any mortgage,
indenture or other instrument under which there may be issued or by which there
may be secured or evidenced any indebtedness for money borrowed by the Company,
whether existing on the date hereof or created subsequent to the date hereof,
which default relates to the obligation to pay the principal of or interest on
any such indebtedness and the effect of such default is to cause such
indebtedness to become due prior to its stated maturity; or

                  (vii) if final judgment(s) for the payment of money in excess
of $200,000 individually or $250,000 in the aggregate shall be rendered against
the Company, and the same shall remain undischarged or unbonded for a period of
thirty (30) consecutive days, during which execution shall not be effectively
stayed.

            B. Remedies. Upon the occurrence of any Event of Default, and at all
times thereafter during the continuance thereof: (i) this Note shall, at the
option of the holder thereof, in accordance with Section 13.11 of the Agreement
(except in the case of Sections 7(A)(iv) and (v) hereof, the occurrence of which
shall automatically effect acceleration, regardless of any action or forbearance
in respect of any prior or ongoing default or event of default which may be
inconsistent with such automatic acceleration), become immediately due and
payable, both as to principal, interest and premium, without presentment,
demand, protest or notice of any kind, all of which are hereby expressly waived,
anything contained herein or in the Agreement to the contrary notwithstanding,
(ii) all outstanding obligations under this Note, and all other outstanding
obligations on which the applicable interest rate is determined by reference to
the interest rate under this Note, shall bear interest at the default rate of
interest provided herein, (iii) the holder of this Note may file suit against
the Company on the Note and/or seek specific performance or injunctive relief
hereunder (whether or not a remedy exists at law or is adequate), (iv) the
holder of this Note shall have the right, in accordance with this Note to
exercise any and all remedies as such holder may determine in such holder's
discretion (without any requirement of marshalling of assets, or other such
requirement).


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<PAGE>

      7. Miscellaneous.

            A. Parties in Interest. All covenants, agreements and undertakings
in this Note binding upon the Company or the Payee shall bind and inure to the
benefit of the permitted successors and assigns of the Company and the Payee,
respectively, whether so expressed or not. Any transferee or transferees of this
Note, by their acceptance hereof, assume the obligations of the Payee in the
Agreement with respect to the conditions and procedures for transfer of this
Note.

            B. Notices. All notices, requests, consents and demands shall be
given or made, and shall become effective, in accordance with the Agreement
executed by the Payee and the Company.

            C. Construction. This Note shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the laws of
the State of New York and any applicable laws of the United States of America,
without giving effect to the conflicts or choice of law principles thereof.

            D. Enforceability. Maker acknowledges that this Note and Maker's
obligations hereunder are and shall at all times continue to be absolute and
unconditional in all respects, and shall at all times be valid and enforceable
irrespective of any other agreements or circumstances of any nature whatsoever
which might otherwise constitute a defense to this Note and the obligations of
Maker evidenced hereby, unless otherwise expressly evidenced in a writing duly
executed by the holder hereof.

            E. Payment. If the date for any payment due hereunder would
otherwise fall on a day which is not a Business Day, such payment or expiration
date shall be extended to the next following Business Day with interest payable
at the applicable rate specified herein during such extension. "Business Day"
shall mean any day other than a Saturday, Sunday, or any day which shall be in
the City of New York a legal holiday or a day on which banking institutions are
authorized by law to close.

            F. Waiver and Set-off. Maker hereby waives diligence, presentment,
demand, protest and notice of any kind whatsoever. The nonexercise by Payee of
any of its rights hereunder in any particular instance shall not constitute a
waiver thereof in that or any subsequent instance. The Payee, in addition to any
other right available to it under applicable law, shall have the right, at its
option, to immediately set off against this Note any monies owed by the Payee in
any capacity to Maker, whether or not due, upon the occurrence of any Event of
Default, even though such charge is made or entered on the books of Payee
subsequent to those events.

            G. Lost Documents. Upon receipt by the Company of evidence
satisfactory to it of the loss, theft, destruction or mutilation of this Note or
any Note exchanged for it, and (i) in the case of loss, theft or destruction, of
indemnity satisfactory to it and (ii) in the case of mutilation, of surrender
for cancellation of such Note, and, in any case, upon reimbursement to the
Company of all reasonable expenses incidental thereto, the Company will make and
deliver


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<PAGE>

in lieu of such Note a new Note of like tenor and principal amount and dated as
of the original date of this Note.


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<PAGE>

      IN WITNESS WHEREOF, this Note has been executed and delivered on the date
specified above by the duly authorized representative of the Company.

                                               MILESTONE SCIENTIFIC INC.


                                               by: _____________________________
                                                    Leonard Osser, Chairman and
                                                    Chief Executive Officer


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