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                                                                   Exhibit 10.20


       John A. Blaeser Options - Full Vesting in the Event of Acquisition
                   of the Company or Termination as a Director


                                                         Option Number B9601-006


                          CONCORD COMMUNICATIONS, INC.

                             Stock Option Agreement



Concord Communications, Inc., a Massachusetts corporation (the "Company"),
hereby grants this 1st day of 1996 to John Blaeser (the "Employee") an Option
(the "Option") to purchase a maximum of 563,139 shares of its Common Stock, $.01
par value, at the price of .05 per share, on the following terms and conditions.

1.       GRANT UNDER 1995 STOCK PLAN

         This Option is granted pursuant to and is governed by the Company's
         1995 Stock Plan (the "Plan") and, unless the context otherwise
         requires, terms used herein shall have the same meaning as in the Plan.
         Determinations made in connection with this Option pursuant to the Plan
         shall be governed by the Plan as it exists on this date. In the event
         of any inconsistency or conflict between this Agreement and the Plan,
         the terms of the Plan shall govern.

2.       OTHER OPTIONS

         This option is in addition to any other Options heretofore or hereafter
         granted to the Employee by the Company, but a duplicate original of
         this instrument shall not effect the grant of another Option.

3.       EXTENT OF OPTION IF EMPLOYMENT CONTINUES

         If the Employee continues to be employed by the Company on the
         following dates, the Employee may exercise this Option for the number
         of shares set forth in the schedule below:



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                         Cumulative                                Cumulative
                           Shares                                    Shares
        Date             Exercisable             Date             Exercisable     
      --------           -----------           --------           -----------
                                                               
      01/01/96              18,396             04/01/98             344,165
      04/01/96              26,045             07/01/98             377,739
      07/01/96              45,402             10/01/98             411,311
      10/01/96              62,905             01/01/99             444,883
      01/01/97             172,092             04/01/99             478,457
      04/01/97             206,506             07/01/99             510,326
      07/01/97             240,921             10/01/99             537,993
      10/01/97             275,337             01/01/00             563,139
      01/01/98             309,751          


Provided, however, this Option shall become exercisable in full upon the first
to occur of the following:

(a)      The consolidation or merger of the Company with or into any other
         entity (other than a consolidation or merger in which the Company is
         the continuing corporation and which does not result in any
         reclassification of, or change in, the outstanding shares of the
         capital stock of the Company), or a sale, conveyance, or disposition of
         all or substantially all of the assets of the Company; and

(b)      The time when the Employee shall cease to be a Director of the Company
         other than by reason of death, disability or resignation.

The foregoing rights are cumulative and, while the Employee continues to be
employed by the Company, may be exercised up to and including the date which is
eight (8) years from the date this Option is granted. All of the foregoing
rights are subject to Sections 4 and 5 below, as appropriate, if the Employee
ceases to be employed by the Company or becomes disabled or dies while in the
employ of the Company.

If the Company becomes a party to a merger, consolidation, reorganization or
similar corporate transaction, the Company agrees to send written notice of such
event to the Employee. The Company agrees to request for the holders of
unexercised Options rights comparable to those granted under the 1995 Plan but
shall incur no liability for failure to secure such rights.

4.       TERMINATION OF EMPLOYMENT

         If the Employee ceases to be employed by the Company other than by
         reason of death, this Option shall terminate after the passage of sixty
         (60) days from the date employment ceases, but in no event later than
         the scheduled expiration date. In such a case, the Employee's only
         rights hereunder shall be those which are properly exercised before the
         termination of this Option.

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5.       DEATH OR DISABILITY

         If the Employee dies while in the employ of the Company, this Option
         may be exercised, to the extent of the number of shares with respect to
         which the Employee could have exercised it on the date of his death, by
         his estate, personal representative, or beneficiary to whom this Option
         has been assigned pursuant to Article 10, at any time within 180 days
         after the date of death, but not later than the scheduled expiration
         date. If the Employee ceases to be employed by the Company by reason of
         his disability (as defined in the Plan), this Option may be exercised
         to the extent of the number of shares with respect to which he could
         have exercised it on the date of the termination of his employment, at
         any time within 180 days after such termination, but not later than the
         scheduled expiration date. At the expiration of such 180 day period or
         the scheduled expiration date, whichever is earlier, this Option shall
         terminate and the only rights hereunder shall be those as to which the
         Option was properly exercised before such termination.

6.       PARTIAL EXERCISE

         Exercise of this Option up to the extent above stated may be made in
         part at any time and from time to time within the above limits, except
         that this Option may not be exercised for a fraction of a share unless
         such exercise is with respect to the final installment of stock subject
         to this option and a fractional share (or cash in lieu thereof) must be
         issued to permit the Employee to exercise completely such final
         installment.

7.       AGREEMENT TO PURCHASE FOR INVESTMENT

         By acceptance of this Option, the Employee agrees that a purchase of
         shares under this Option will not be made with a view to their
         distribution, as that term is used in the Securities Act of 1933, as
         amended, unless in the opinion of counsel to the Company such
         distribution is in compliance with or exempt from the registration and
         prospectus requirements of the Act, and the Employee agrees to sign a
         certificate to such effect at the time of exercising this Option and
         agrees that the certificate for the shares so purchased may be
         inscribed with a legend to ensure compliance with the Act and with any
         applicable state securities laws.

8.       METHOD OF EXERCISING OPTION

         Subject to the terms and conditions of this Agreement, this Option may
         be exercised by written notice to the Company, at the principal
         executive office of the Company, or to such transfer agent as the
         Company shall designate. Such notice shall state the election to
         exercise this Option and the number of shares in respect of which it is
         being exercised and shall be signed by the person or persons so
         exercising this Option. Such notice shall be accompanied by payment of
         the full purchase price of such shares, and the Company shall deliver a
         certificate or certificates representing such shares as soon as
         practicable after the notice and payment have been received. The
         certificate or certificates for the 

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         shares as to which this Option shall have been so exercised shall be
         registered in the name of the person or persons so exercising this
         Option (or, if this Option shall be exercised by the Employee and if
         the Employee shall so request in the notice exercising this Option,
         shall be registered in the name of the Employee and another person
         jointly, with right of survivorship) and shall be delivered as provided
         above to or upon the written order of the person or persons exercising
         this Option. In the event this Option shall be exercised, pursuant to
         Section 5 hereof, by any person or persons other than the Employee,
         such notice shall be accompanied by appropriate proof of the right of
         such person or persons to exercise this Option. All shares that shall
         be purchased upon the exercise of this Option as provided herein shall
         be fully paid and nonassessable.

9.       OPTION NOT TRANSFERABLE

         This Option is not transferable or assignable except by will or by the
         laws of descent and distribution. During the Employee's lifetime,
         only the Employee can exercise this Option.

10.      NO OBLIGATION TO EXERCISE OPTION

         The grant and acceptance of this Option imposes no obligation on the
         Employee to exercise it.

11.      NO OBLIGATION TO CONTINUE EMPLOYMENT

         The Company is not by the Plan or this Option obligated to continue the
         Employee in employment.

12.      NO RIGHTS AS STOCKHOLDER UNTIL EXERCISE

         The Employee shall have no rights as a stockholder with respect to
         shares subject to this Agreement until a stock certificate therefor has
         been issued to the Employee and is fully paid for. Except as is
         expressly provided in the Plan with respect to certain changes in the
         capitalization of the Company, no adjustment shall be made for
         dividends or similar rights for which the record date is prior to the
         date such stock certificate is issued.

13.      CAPITAL CHANGES AND BUSINESS SUCCESSIONS

         It is the purpose of this Option to encourage the Employee to work for
         the best interest of the Company and its stockholders. Since, for
         example, that might require the issuance of a stock dividend or a
         merger with another corporation, the purpose of this Option would not
         be served if such a stock dividend, merger, or similar occurrence would
         cause the Employee's rights hereunder to be diluted or terminated and
         thus be contrary to the Employee's interest. The Plan contains
         extensive provisions designed to preserve Options at full value in a
         number of contingencies. Therefore, provisions in the Plan for
         adjustments with respect to stock subject to Options and the related
         provisions with 

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         respect to successors to the business of the Company are hereby made
         applicable hereunder and are incorporated herein by reference. In
         particular, without limiting the generality of the foregoing, it is
         understood that for the purposes of Sections 3 and 5 hereof, both
         inclusive, employment by the Company includes employment by a related
         corporation as described in the Plan.

14.      EARLY DISPOSITION

         The Employee agrees to notify the Company of any disposition of any
         shares of Common Stock acquired on the exercise of this Option within
         the two year period beginning on the date of grant or within one year
         after the date of the transfer of such shares to the Employee. The
         Employee also agrees to provide the Company with any information which
         it shall request concerning any such disposition. Employees who receive
         incentive stock options will be disqualified under Section 422 of the
         Code from receiving the favorable income tax treatment otherwise
         available with respect to the exercise of such an Option if they
         dispose of the stock received on exercise of the Option within either
         of the one or two year periods described in the preceding sentence.

15.      GOVERNING LAW

         This Agreement shall be governed by and interpreted in accordance with
         the internal laws of Massachusetts.

IN WITNESS WHEREOF the Company and the Employee have caused this instrument to
be executed, and the Employee whose signature appears below acknowledges receipt
of a copy of the Plan and acceptance of an original copy of this Agreement.


                                             CONCORD COMMUNICATIONS, INC.


                                             By: /s/
                                                 -------------------------------

                                             /s/ John A. Blaeser
                                             -----------------------------------
                                                         EMPLOYEE