SIXTH AMENDMENT TO LEASE


                This is a Sixth  Amendment  to Lease dated as of January 1, 1996
between John Hancock Mutual Life Insurance Company ("Landlord") and Kronos
Incorporated ("Tenant").


                       W I T N E S S E T H:


WHEREAS,  Landlord and Tenant  entered into a lease dated  November 6, 1992,  as
amended by a First Amendment dated November 6, 1992, a Second Amendment dated
June, 1994, a Restated Third Amendment dated as of October 30, 1994, a Fourth 
Amendment dated as of June 1, 1995, and a Fifth Amendment dated as of 
June 28, 1995, of premises ("Premises") in a building ("Building") located
at 400 Fifth Avenue, Waltham, Massachusetts ("Lease"); and

WHEREAS,  Landlord  and Tenant  have  agreed to amend the Lease to incorporate
additional space on the terms and conditions more particularly set forth below.

NOW, THEREFORE, for good and valuable consideration, and in consideration of 
the covenants and agreements herein contained, the parties hereby agree to
amend the Lease as follows:

     1.The plan attached  hereto as Exhibit A-3,  setting forth the  approximate
location of 762 square feet on the 1st floor of the  Building to be added to the
Premises pursuant to this Sixth Amendment ("Sixth Amendment  Additional Space"),
is hereby incorporated into Exhibit A to the Lease.


     2.The term  "Leased  Premises" in Section 1 of the Lease is here by amended
by deleting therefrom the phrase "70,112 rentable square feet", and substituting
therefor the phrase "70,874 rentable square feet".


     3.The  definition  of "Minimum  Annual  Rent" set forth in Section 1 of the
Lease is hereby  amended by  deleting  the same and  substituting  therefor  the
following:




"MINIMUM ANNUAL RENT:

Year                        Sq. Ft.                     Per RSF                       Total

                                                                                  
4/1/93-                     62,340                      10.95*                     $682,623.00
3/31/94

4/1/94-                     62,340                      14.75*                     919,515.00
10/31/94                                                                           annual rate;
                                                                                   536,383.75 for this
                                                                                   7-month period

11/1/94-                    62,340                      14.75*                     979,023.00
3/31/95                      3,480                      17.10                      annual rate; 407,926.25
                                                                                   for this 5-month period

4/1/95-                     62,340                      15.00                      994,608.00 annual rate;
5/31/95                      3,480                      17.10                      165,768.00 for this
                                                                                   2-month period
6/1/95-                     62,340                      15.00                      1,076,156.00 annual
1/31/96                      3,480                      17.10                      rate; 717,437.33 for
                             4,292                      19.00                      this 8-month period

2/1/96-                     62,340                      15.00                      1,091,357.90
3/31/96                      3,480                      17.10                      annual rate; 181,892.98
                             4,292                      19.00                      for this 2-month period
                               762                      19.95

4/1/96-                     62,340                      15.25                      1,106,942.90
3/31/97                      3,480                      17.10
                             4,292                      19.00
                               762                      19.95

4/1/97-                     62,340                      16.25                      1,169,282.90
3/31/98                      3,480                      17.10
                             4,292                      19.00
                               762                      19.95

4/1/98-                     62,340                      17.00                      1,216,037.90
3/31/99                      3,480                      17.10
                             4,292                      19.00
                               762                      19.95

4/1/99-                     62,340                      17.00                      1,216,037.90
3/31/00                      3,480                      17.10
                             4,292                      19.00
                               762                      19.95

*Except as modified by the terms of Section 36."



     4. The term "Total  Rentable  Area of the Leased  Premises" in Section 1 of
the Lease is hereby  amended  by  deleting  therefrom  "70,112  sq.  feet",  and
substituting therefor "70,874 sq. feet".


     5. The term "Tax  Base" in  Section 1 of the  Lease is  hereby  amended  by
adding thereto the following:

         "Notwithstanding the foregoing, the Tax Base for the Sixth Amendment
         Additional Space shall be Tax Year 1996."

     6. The terms "Tax  Percentage" and "Operating Cost Percentage" in Section 1
of the Lease are hereby amended by adding thereto the following:

         ", and, as to the Sixth Amendment Additional Space, .63%"


     7. The term  "Operating  Cost Base" is hereby amended by adding thereto the
following:


         "Notwithstanding the following, the Operating Cost Base for the Sixth
          Amendment Additional Space shall be Calendar Year 1996."


     8. The Sixth Amendment  Additional Space shall be deemed to be incorporated
into the Lease as of  February  1,  1996,  and from and  after  that  date,  the
Premises  shall be deemed to include the  original  premises  demised  under the
Lease and the Sixth Amendment  Additional  Space, in accordance with and subject
to all of the terms and  provisions  of the  Lease.  Accordingly,  the  Tenant's
rights to the Sixth  Amendment  Additional  Space shall expire as of the date of
expiration of the Lease, or its earlier  termination.  Any exercise by Tenant of
its  option to extend the Lease in  accordance  with  Section  38 thereof  shall
include the Sixth Amendment Additional Space.


     9.  Tenant  hereby   acknowledges  and  agrees  that  the  Sixth  Amendment
Additional  Space shall be  delivered  by Landlord to Tenant in its "as is, with
all faults" condition,  and that Landlord shall have no obligations with respect
to improvement of the Sixth Amendment  Additional  Space.  Nothwithstanding  any
provision  hereof  to the  contrary,  (a)  this  Sixth  Amendment  shall  not be
effective until the existing occupant has vacated the Sixth Amendment Additional
Space,  (b) Tenant  shall have no claim  against  Landlord in the event that the
space is not available as of February 1, 1996, and (c) Tenant's  occupancy shall
at all times be subject to all of the terms and conditions of the Lease.


     10. Landlord and Tenant hereby represent and warrant to each other that the
only broker  with whom each of them has had  dealings  in  connection  with this
Sixth  Amendment  is Beacon  Management  Company.  Each party  agrees to defend,
indemnify  and hold the other party  harmless  from any breach of the  foregoing
representation.

    Except as  hereinabove  amended,  the Lease  remains  in full force and
effect.

    EXECUTED  as a sealed  instrument  as of the day and year  first  above
written.
                                                     LANDLORD:
                                                     JOHN HANCOCK MUTUAL LIFE
                                                     INSURANCE COMPANY


                                                     By: /s/ M.E. Armour
                                                              Its:

                                                     TENANT:
                                                     KRONOS INCORPORATED


                                                     By: /s/Paul Lacy
                                                              Its:

                                                     V.P., Finance and
                                                       Administration




                                   EXHIBIT A - 3

Exhibit A-3 contains a graphic which sets forth the approximate  location of 762
square  feet on the  first  floor of the  Building  to be added to the  Premises
pursuant to the Sixth Amendment to the Lease.