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                                                                   Exhibit 10.43


                              Bio-Plexus, Inc.
                             129 Reservoir Road
                              Vernon, CT 06066

                                                                   April 3, 2000

Appaloosa Investment Limited
  Partnership I
26 Main Street, 1st Floor
Chatham, New Jersey 07928
Attention:  Mr. James Bolin

Dear Mr. Bolin:

          Reference is made to the 7.5% Secured Note, dated October 21, 1999,
issued by Bio-Plexus, Inc. (the "Company") to Appaloosa Investment Limited
Partnership I ("Appaloosa") (as such 7.5% Secured Note may be amended and
restated from time to time, the "7.5% Note"), the 15% Secured Note, dated
January 5, 2000, issued by the Company to Appaloosa (as such 15% Secured Note
may be amended and restated from time to time, the "15% Note"), and the side
letter, dated December 30, 1999, between the Company and Appaloosa (the "First
Side Letter"). The purpose of this letter is to set forth the understanding of
the Company and Appaloosa with respect to the matters set forth herein:

          (a)       on the date hereof, the Company and Appaloosa will enter
                    into a second amendment to the 7.5% Note in the form
                    attached hereto as Exhibit A;

          (b)       on the date hereof, the Company and Appaloosa will enter
                    into a first amendment to the 15% Note in the form attached
                    hereto as Exhibit B;

          (c)       on the date hereof, the Company and Appaloosa will enter
                    into the 15% Secured Note in the form attached hereto as
                    Exhibit C (the "Third Bridge Note"); and
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          (d)       paragraph (d) of the First Side Letter is hereby amended by
                    deleting it in its entirety and substituting in lieu thereof
                    the following:

                    (d) (i) On the closing date of the Rollover Transactions
          (but only if the Company has hired a new Chief Executive Officer
          approved by Appaloosa in its sole discretion by that date), the $3
          Warrants (as defined in the 7.5% Note) will be, at the election of
          Appaloosa, cancelled and be of no further force and effect and,
          simultaneously therewith, the Company will issue to one or more
          affiliates of Appaloosa replacement warrants to purchase 1,000,000
          shares of Common Stock with an exercise price of $4 per share in the
          form attached hereto as Exhibit D (if so issued, the "Warrants"). If
          the Company has not hired a new Chief Executive Officer approved by
          Appaloosa in its sole discretion by the closing date of the Rollover
          Transactions (or if the Company has hired a new Chief Executive
          Officer approved by Appaloosa by the closing date of the Rollover
          Transactions but Appaloosa elected not to exchange the $3 Warrants for
          the Warrants at that time), the $3 Warrants shall be exchanged for the
          Warrants six months and one day after the closing date of the Rollover
          Transactions (and Appaloosa hereby agrees not to exercise any of the
          $3 Warrants during such period).

                        (ii) If the Rollover Transactions are not consummated
          for any reason, the $3 Warrants (as defined in the 7.5% Note) will
          remain in full force and effect and the terms and conditions thereof
          will remain unchanged.

          The Company represents that (i) the execution and delivery of this
letter by the Company and the performance by it of the transactions contemplated
hereby (including, without limitation, the issuance of the Warrants and issuance
of shares of Common Stock (as defined in the 7.5% Note) upon exercise of the
Warrants) and compliance by the Company with all the provisions of the Warrants
(as applicable) have been duly authorized by all requisite corporate proceedings
on the part of the Company and (ii) the shares of Common Stock issuable upon
exercise of the Warrants have been validly reserved for issuance, and upon
issuance, will be validly issued and outstanding, fully paid and nonassessable.

          The Company cannot assign its rights and obligations under this letter
without the written consent of Appaloosa.

          Appaloosa represents that (a) it is acquiring the Third Bridge Note
for its own account for the purpose of investment and not with a view to or for
sale in connection with any distribution thereof except in compliance with all
applicable securities law and (b) it is an "accredited
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investor" within the meaning of Rule 501 promulgated under the Securities Act of
1933, as amended.

          If any term, provision, covenant or restriction of this letter or any
exhibit hereto is held by a court of competent jurisdiction to be invalid, void
or unenforceable, the remainder of the terms, provisions, covenants and
restrictions of this letter and such exhibits shall remain in full force and
effect and shall in no way be affected, impaired or invalidated. It is hereby
stipulated and declared to be the intention of the parties that they would have
executed the remaining terms, provisions, covenants and restrictions without
including any of such which may be hereafter declared invalid, void or
unenforceable.

          Appaloosa, on the one hand, and the Company, on the other, acknowledge
and agree that irreparable damage would occur in the event that any of the
provisions of this letter were not performed in accordance with their specific
terms or were otherwise breached. It is accordingly agreed that Appaloosa shall
be entitled to an injunction to prevent breaches of the provisions of this
letter and to enforce specifically the terms and provisions hereof in any court
of the United States or any state thereof having jurisdiction, this being in
addition to any other remedy to which they may be entitled at Law (as defined in
the 7.5% Note) or equity.

          Neither the Company nor Appaloosa shall make any public statements,
including, without limitation, any press releases, with respect to this letter
and the transactions contemplated hereby without the prior written consent of
the other party (which consent shall not be unreasonably withheld) except as may
be required by Law. If a public statement is required to be made by Law, the
parties shall consult with each other in advance as to the contents and timing
thereof.

          This letter shall not constitute an amendment of any other provisions
of the First Side Letter not expressly referred to herein and shall not be
construed as a waiver or consent to any further or future action on the part of
the Company that would require a waiver or consent of the Holder. Except as
expressly amended hereby, the provisions of the First Side Letter shall remain
in full force and effect.

          THIS LETTER SHALL BE CONSTRUED AND ENFORCED IN ACCORDANCE WITH, AND
THE RIGHTS OF THE PARTIES SHALL BE GOVERNED BY, THE LAW OF THE STATE OF NEW YORK
EXCLUDING CHOICE-OF-LAW PRINCIPLES OF THE LAW OF SUCH STATE THAT WOULD REQUIRE
THE APPLICATION OF THE LAWS OF A JURISDICTION OTHER THAN SUCH STATE.

          If any Litigation (as defined in the 7.5% Note) shall be brought by
Appaloosa in order to enforce any right or remedy under this letter, the Company
hereby consents and will submit to the jurisdiction of any state
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or federal court of competent jurisdiction sitting within the area comprising
the Southern District of New York on the date of this letter. The Company hereby
irrevocably waives any objection, including, but not limited to, any objection
to the laying of venue or based on the grounds of forum non conveniens, which it
may now or hereafter have to the bringing of any such Litigation in such
jurisdiction.

          THE COMPANY HEREBY WAIVES ANY RIGHT IT MAY HAVE TO A TRIAL BY JURY IN
RESPECT OF ANY ACTION, PROCEEDING OR LITIGATION DIRECTLY OR INDIRECTLY ARISING
OUT OF, UNDER OR IN CONNECTION WITH, THIS LETTER.
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          Please confirm that the foregoing is in accordance with your
understanding by signing and returning to me this letter, whereupon this letter
shall be deemed accepted and binding.


                                          Very truly yours,

                                          BIO-PLEXUS, INC.


                                          By:/s/ Carl R. Sahi
                                             ------------------------------
                                             Name:    Carl R. Sahi
                                             Title:   President and Chief
                                                      Executive Officer



ACCEPTED AND AGREED
THIS 3rd DAY OF APRIL 2000

APPALOOSA INVESTMENT LIMITED
  PARTNERSHIP I

By: Appaloosa Management L.P., its
      General Partner
By: Appaloosa Partners Inc., its
      General Partner


By:/s/ James E. Bolin
   ----------------------------------
   Name:   James E. Bolin
   Title:  Vice President