EXHIBIT 3
April 26, 1997
 
                        [Letterhead of BBN Corporation]
 
GTE Corporation
1 Stamford Forum
Stamford, CT 06901-3516
 
                           CONFIDENTIALITY AGREEMENT
 
Ladies and Gentlemen:
 
  In connection with your possible interest in a transaction (the
"Transaction") involving BBN Corporation (the "Company"), it is likely that
technical and financial information and other information of a confidential or
proprietary nature will be disclosed by both parties, their respective
subsidiaries and affiliates. All such information (whether written or oral)
furnished by either party's directors, officers, employees, affiliates,
representatives, (including, without limitation, financial advisors, attorneys
and accountants) or agents (collectively, "Representatives") to the other
party and all analyses, compilations, forecasts, studies, or other documents
prepared by either party or its Representatives in connection with its or
their review of, or its interest in, the Transaction which contain or reflect
any such information is hereinafter referred to as the "Information". The term
Information will not, however, include information which (i) is or becomes
publicly available other than as a result of a disclosure by the receiving
party or its Representatives or (ii) is or becomes available to the receiving
party on a nonconditional basis from a source (other than the disclosing party
or its Representatives) which, to the best of the receiving party's knowledge
after due inquiry, is not prohibited from disclosing such information to the
receiving party by a legal, contractual, or fiduciary obligation.
 
Accordingly, it is hereby agreed:
 
  1. Each party and its Representatives (i) will keep the Information received
from the other party confidential and will not (except as required by
applicable law, regulation, or legal process, and only after compliance with
paragraph 3 below), without the prior written consent of the disclosing party,
disclose any Information in any manner whatsoever, and (ii) will not use any
Information other than in connection with the evaluation of a Transaction;
provided, however, that the receiving party may reveal the Information to its
Representatives (a) who need to know the Information for the purpose of
evaluating the Transaction, (b) who are informed by the receiving party of the
confidential nature of the Information, and (c) who agree to act in accordance
with the terms of this letter agreement. Each party will cause its
Representatives to observe the terms of this letter agreement, and each party
will be responsible for any breach of this letter agreement by any of its
Representatives.
 
  2. Each party and its Representatives will not (except as required by
applicable law, regulation, or legal process), without the prior written
consent of the other party, disclose to any person the fact that the
Information exists or has been made available, that the parties are or
negotiations are taking or have taken place concerning the Transaction or
involving the Company or any term, condition, or other fact relating to the
Transaction or such discussions or negotiations, including, without
limitation, the status thereof.
 
  3. In the event that either party or any of their Representatives is
requested pursuant to, or required by, applicable law, regulation or legal
process to disclose any of the Information, that party will notify the other
promptly so that it may seek a protective order or other appropriate remedy
or, in its sole discretion, waive compliance with the terms of this letter
agreement.
 
  4. If either party determines not to proceed with the Transaction, that
party will promptly inform the other party of that decision and, in that case,
and at any time upon the request of either party or any of their
Representatives, the party having such Information will, at its option, either
(i) promptly destroy all copies of the written Information in their or their
Representatives' possession and confirm such destruction to the other party in
writing, or (ii) promptly deliver to the other party all copies of the written
Information in its or its Representatives' possession. All Information,
including any oral Information will continue to be subject to the terms of
this letter agreement.
 

 
  5. The parties acknowledge that neither party or its Representatives, nor
any of their respective officers, directors, employees, agents, or controlling
persons within the meaning of Section 20 of the Securities Exchange Act of
1934, as amended, makes any express or implied representation or warranty as
to the accuracy or completeness of the Information, and the parties or
omissions therefrom. The parties further agree that they are not entitled to
rely on the accuracy or completeness of the Information and that they will be
entitled to rely solely on such representations and warranties as may be
included in any definitive agreement with respect to the Transaction, subject
to such limitations and restrictions as may be contained therein.
 
  6. Each party is aware, and will advise its Representatives who are informed
of the matters that are the subject of this letter agreement, of the
restrictions imposed by the United States securities laws on the purchase or
sale of securities by any person who has received material, non-public
information from the issuer of such securities and on the communication of
such Information to any other person when it is reasonably foreseeable that
such other person is likely to purchase or sell such securities in reliance
upon such Information.
 
  7. Each party will not for one year from the date hereof, directly or
indirectly, unless specifically requested or approved in writing in advance by
an executive officer of the Board of Directors of the other party, which
approval, in the case of subparagraph (i) below, shall not be unreasonably
withheld or delayed (in either case such other party being referred to for
purposes of this paragraph as the "Other Party"):
 
    (i) acquire or agree, offer, seek, or propose to acquire (or request
  permission to do so), ownership (including, but not limited to, beneficial
  ownership as defined in Rule 13d-3 under the Exchange Act) of substantially
  all of the Other Party's assets or businesses or in excess of 5% of the
  outstanding voting securities issued by the Other Party, or any rights or
  options to acquire such ownership (including from a third party), or
 
    (ii) directly or indirectly solicit or try to induce any employee of the
  Other Party to leave that employment, or agree to employ or to employ
  anyone who is at the time of such action, or was within the three month
  period prior thereto, an employee of the Other Party or any of its
  subsidiaries.
 
  Notwithstanding the foregoing, (a) the terms of the above subparagraph (i)
shall be null and void (A) upon the execution of a contract between the
parties hereto with respect to the Transaction or (B) in the event the Other
Party fails to negotiate in good faith with respect to the Transaction and any
agreement pertaining thereto or (C) if another person engages in any activity
(or comparable activity) in which a party would be precluded from engaging by
reason of this letter agreement or otherwise, or if another person proposes or
announces an intention to engage in such activity (or comparable activity),
and (b) the terms of the above subparagraph (i) shall not be applicable to the
purchase and sale of any securities of either party by independent third-party
managers of pension or other employee benefit plans who have not received any
of the Information and who are acting as passive investors.
 
  8. The parties acknowledge that remedies at law may be inadequate to protect
against any actual or threatened breach of this letter agreement by either
party or by its Representatives, and, without prejudice to any rights and
remedies otherwise available to the non-breaching party, the breaching party
agrees to the granting of injunctive relief in favor of the non-breaching
party without proof of actual damages.
 
  9. No failure or delay by a party in exercising any right, power or
privilege hereunder will operate as a waiver thereof, nor will single or
partial exercise thereof preclude any other or further exercise thereof or the
exercise of any right, power or privilege hereunder.
 
 
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  10. This letter agreement will be governed by and construed in accordance
with the laws of the Commonwealth of Massachusetts applicable to contracts
between residents of that state and executed in and to be performed in that
state.
 
  11. This letter agreement contains the entire agreement between you and us
concerning the confidentiality of the Information, and no modifications of
this letter agreement or waiver of the terms and conditions hereof will be
binding upon you or us, unless approved in writing by each of you and us.
 
  Please confirm your agreement with the foregoing by signing and returning to
the undersigned the duplicate copy of this letter enclosed herewith.
 
                                          Very truly yours,
 
                                          BBN CORPORATION
 
                                                    /s/ John Montjoy
                                          By: _________________________________
 
                                                      John Montjoy
                                          Name: _______________________________
 
                                                  Senior Vice President
                                          Title: ______________________________
 
Accepted and Agreed as of the
date first written above:
 
GTE CORPORATION
 
         /s/ Marianne Drost
By: _________________________________
 
           Marianne Drost
Name: _______________________________
 
              Secretary
Title: ______________________________
 
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