Exhibit 4.2
                                                                     -----------

                      AMENDMENT NO. 1 TO RIGHTS AGREEMENT

     This Amendment No. 1 to Rights Agreement ("Amendment No. 1") is made by and
between Cytyc Corporation, a Delaware corporation (the "Company"), and
BankBoston, N.A., as Rights Agent (the "Rights Agent") as of the 22nd day of
June, 1998. Reference is made to the Rights Agreement dated as of August 27,
1997 (the "Agreement") between the parties. Capitalized terms not defined herein
shall have the respective meaning ascribed to them in the Agreement.

     In accordance with Section 27 of the Agreement, the Company hereby desires
to amend the Agreement as follows:

     1.  Effective immediately, the Rights Agreement is hereby amended to (i)
delete all references to "Continuing Director" or "Continuing Directors" and
inserting in place thereof "Director" or "Directors" and (ii) delete Section
1(o) in its entirety.

     2.  Except as specifically amended and set forth herein, the Agreement
shall remain unchanged and in full force and effect in accordance with its
terms.

     3.  By execution of this Amendment No. 1, the Company hereby certifies to
the Rights Agent that the amendments to the Agreement reflected herein comply
with Section 27 of the Agreement.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 1 to
be executed and delivered as of the date first written above.


                              CYTYC CORPORATION

                                   /s/ Patrick J. Sullivan
                              By: ___________________________
                              Name:   Patrick J. Sullivan
                              Title:  President and Chief Executive 
                                      Officer

                              BANKBOSTON, N.A., as Rights Agent

                                   /s/ Tyler Haynes 
                              By: ___________________________
                              Name:   Tyler Haynes
                              Title:  Administration Manager