Document:

June 30, 2000

Mr. Richard Kumpf
12 Whidhita Road
Medfield, MA 02052

Dear Richard:

     I am pleased to offer you the position of Vice President of Engineering
with Zoom Telephonics, Inc. (hereafter referred to as the Company). The details
of the offer are listed below:

     o    $150,000 annual starting salary.

     o    $40,000 starting bonus.

     o    $20,000 end-of-year performance-based bonus.

     o    Issuance of Shares of Common Stock. Employee will be entitled to
          purchase that number of shares of the Company's Common Stock equal to
          $150,000 divided by the closing price of the Common Stock as quoted
          on the Nasdaq National Market on Employee's first day of work with
          the Company (the "Shares"). The purchase price for the Shares will be
          $.01 per share (the "Purchase Price"). The Shares will be subject to
          the terms of a restricted stock repurchase agreement pursuant to
          which the Company will have the option to repurchase the Shares from
          the Employee for the original Purchase Price if the Employee ceases
          to be employed by the Company because of Employee's termination for
          gross misconduct or voluntary resignation prior to January 1, 2002.
          Until January 1, 2002, the Shares will be held in escrow by the
          Company to secure the Employee's obligation to resell the Shares to
          the Company in accordance with the terms and conditions of the
          restricted stock repurchase agreement. The restricted stock
          repurchase agreement will be executed by the Company and Employee on
          the Employee's first day of work with the Company. The Agreement will
          provide that immediately prior to and subject to the closing of an
          Acquisition of Zoom (i.e., a merger or consolidation of Zoom with or
          into another corporation or the sale, lease or exchange of all or
          substantially all of the assets of Zoom), Richard will be entitled to
          the shares free to the Company's repurchase.

     o    40,000 options granted within 30 days from your date of hire. The
          options would be issued at the market closing price for Zoom stock on
          the day of the issue. The options give you the right (but not the
          obligation) to purchase shares of Company stock at the option price.
          The options expire 36 months from the issue date. You may exercise
          (buy Company stock at the option price) 50% of the options one year
          from the issue date and the final 50%, 24 months from the issue date.
          You can retain the options and exercise them anytime after they have
          vested until they expire.

     o    20,000 additional options will be granted 1 year from your date of
          hire at the market price at the time of the grant.

     o    Options will be granted after the 1st year of employment so you will
          have at least 20,000 options vesting per year during your first 4
          years at Zoom.

     o    If Zoom is acquired, your options will vest automatically.

     As a salaried employee you will receive 4 weeks of paid vacation per year.
There are ten (10) paid holidays per year, and there are up to six (6) sick
days per year.

     You will receive the Company standard benefits package, including medical
and dental insurance, long term disability insurance, and life insurance equal
to one time your annual base salary.

     It is our understanding that all Company proprietary information will be
held in confidence, and will not be conveyed to anyone except as needed for you
to perform your assignment. We further understand that prior employers have no
restrictions that would prohibit, or otherwise restrict, your employment with
the Company. As part of this understanding, you will be asked to sign an
Intellectual Property and Confidentiality Agreement on your first day of
employment.

     You agree that during your employment and for 12 months thereafter, you
will not, directly or indirectly, solicit or encourage any Company employee to
leave its employment and will not employ or otherwise engage any Company
employee to work for any entity in which you have any ownership, interest or a
management or executive position.

     This offer is contingent upon your satisfaction of the requirements of the
Immigration Reform and Control Act of 1986. A valid driver's license and social
security card, or a birth certificate, current passport or other form of
identification will be required as proof of your authorization to work in the
United States.

     This offer is being made to you in writing in order that both you and the
Company will have a written record of the terms and your acceptance of this
offer of employment. Your employment with the Company may be terminated by you
or the Company, without liability to either, with or without cause and with or
without prior notice.

     It is understood that if you choose to leave Zoom within one year of the
start or your employment, you will refund the starting bonus back to Zoom
within 30 days of your leaving. If Zoom terminates you, on the other hand, you
would not repay the signing bonus.

     The terms of your employment may be changed only by written agreement and
signed by you and an authorized representative of the Company. Your employment
will also be subject to the provisions of the Company's Employee Handbook, as
amended from time to time. Please understand that Zoom may need to assign you
to a variety of programs or task as the need arises.

     If this offer is acceptable to you, please date and sign below, and return
a signed copy marked "Attn: Karen Player, Human Resources, Personal and
Confidential".

Sincerely,

Frank Manning
President

The foregoing is accepted as of                    , 2000.

        (Name)EXHIBIT 4.1

                           RIGHTS AGREEMENT AMENDMENT

     This  Rights  Agreement  Amendment,   dated  as  of  March  1,  2000  (this
"Amendment"),  to the Rights  Agreement,  dated as of June 12, 1998 (the "Rights
Agreement"),  between Biopool  International,  Inc., a Delaware corporation (the
"Company") and American  Stock  Transfer & Trust  Company,  as Rights Agent (the
"Rights Agent").

     The Company and the Rights Agent have heretofore executed and delivered the
Rights Agreement.  Pursuant to Section 28 of the Rights  Agreement,  the Company
and the  Rights  Agent may from  time to time  supplement  or amend  the  Rights
Agreement in accordance with the provisions of Section 28 thereof.

     In consideration of the foregoing  premises and mutual agreements set forth
in the Rights  Agreement,  as amended,  and this  Amendment,  the parties hereto
agree as follows:

     1.   The  definition  of  "Acquiring  Person"  in  Section 1 of the  Rights
Agreement is hereby amended and restated to read in its entirety as follows:

               "`Acquiring  Person'  shall mean (i) any  Person (as  hereinafter
          defined) who is an Adverse Person (as  hereinafter  defined),  or (ii)
          any Person who or which,  together with all Affiliates (as hereinafter
          defined)  and  Associates  (as  hereinafter  defined) of such  Person,
          shall,  subsequent  to the  Declaration  Date,  become the  Beneficial
          Owners (as hereinafter defined) of 15% or more of the shares of Common
          Stock then outstanding, but shall not include (x) an Exempt Person (as
          hereinafter  defined) or (y) any Person who becomes a Beneficial Owner
          of 15% or more of the share of Common  Stock then  outstanding  solely
          because  (1) of a change in the  aggregate  number of shares of Common
          Stock  outstanding  since the last date on which such Person  acquired
          Beneficial Ownership of any shares of Common Stock, or (2) it acquired
          such  Beneficial   Ownership  in  the  good  faith  belief  that  such
          acquisition would not (A) cause such Beneficial  Ownership to equal or
          exceed 15% of the shares of Common Stock then  outstanding (or, in the
          case  of  Xtrana,  Inc.,  a  Delaware  corporation   ("Xtrana"),   the
          percentage Xtrana may hold without ceasing to be an Exempt Person) and
          such Person  relied in good faith in computing  the  percentage of its
          Beneficial  Ownership  on publicly  filed  reports or documents of the
          Company which are inaccurate or out-of-date,  or (B) otherwise cause a
          Distribution  Date or the  adjustment  provided  for in  Section 14 to
          occur. Notwithstanding clause (y) of the prior sentence, if any Person
          that is not an  Acquiring  Person  because  of the  operation  of such
          clause  (y) does not  reduce  its  Beneficial  Ownership  of shares of
          Common  Stock  to less  than  15%  (or,  in the  case of  Xtrana,  the
          percentage  Xtrana may hold without ceasing to be an Exempt Person) by
          the close of business on the fifth  Business Day after notice from the
          Company  (the date of notice  being the first day) that such  Person's
          Beneficial  Ownership of Common stock so equals or exceeds 15% (or, in
          the case of Xtrana, the percentage Xtrana. may hold without ceasing to
          be an  Exempt  Person),  such  Person  shall,  at the end of such five
          Business Day period,  become an Acquiring Person (and clause (y) shall
          no longer apply to such Person). For purposes of this definition,  the
          determination  whether  any  Person  acted  in "good  faith"  shall be
          conclusively determined by the Board of Directors, acting by a vote of
          those  directors of the Company  whose  approval  would be required to
          redeem the Rights under Section 25."

<PAGE>

     2.   The definition of "Exempt Person" in Section 1 of the Rights Agreement
is hereby amended and restated to read in its entirety as follows:

               "`Exempt  Person'  shall  include  (i)  the  Company,   (ii)  any
          Subsidiary (as hereinafter defined) of the Company, (iii) any employee
          benefit plan of the Company or any of its Subsidiaries,  or any entity
          holding  shares of Common  Stock  which was  organized,  appointed  or
          established  by the  Company or any  Subsidiary  of the Company for or
          pursuant to the terms of any such plan and (iv) Xtrana, so long as its
          aggregate  Beneficial  Ownership of Common Stock does not exceed 19.9%
          of Common  Stock  then  outstanding,  and so long as  Xtrana  does not
          acquire  any  additional  shares of Common  Stock or commence a tender
          offer or an  exchange  offer for  additional  shares of Common  Stock,
          other than in  connection  with the merger  described  in that certain
          Letter of Intent, dated March 10, 2000, between the Company and Xtrana
          (the "Letter of Intent")."

     3.   Section  3(a) of the  Rights  Agreement  is  amended  by  adding a new
sentence as the final  sentence  thereto,  which  shall read in its  entirety as
follows:

               "Notwithstanding   anything  in  this  Rights  Agreement  to  the
          contrary,  a  Distribution  Date shall not be deemed to have  occurred
          solely as a result of (i) the  approval,  execution or delivery of the
          Merger  Agreement  described  in the  Letter  of Intent  (the  "Merger
          Agreement")  or any of the  agreements or  instruments  required to be
          executed  and   delivered   in   connection   with  the   transactions
          contemplated  therein,  or (ii) the  consummation  of the  Merger  (as
          defined in the Merger Agreement)."

     4.   This Amendment  shall be governed by and construed in accordance  with
the laws of the State of Delaware.

     5.   This Amendment may be executed in any number of counterparts  and each
of such counterparts shall for all purposes be deemed an original,  and all such
counterparts shall together constitute but one and the same instrument.

     6.   Except as expressly  set forth  herein,  this  Amendment  shall not by
implication or otherwise  alter,  modify,  amend or in any way affect any of the
terms, conditions,  obligations, covenants or agreements contained in the Rights
Agreement,  all of which are  ratified  and  affirmed in all  respects and shall
continue in full force and effect.

                                       2

<PAGE>

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

                                       BIOPOOL INTERNATIONAL, INC.

                                       By:    /s/ JOHN H. WHEELER
                                              ----------------------------------
                                       Title: Chief Executive Officer

                                       AMERICAN STOCK TRANSFER & TRUST COMPANY

                                       By:    /s/ WILBERT MYLES
                                              ----------------------------------
                                       Title: Vice President

                                       3

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