UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 6)*


                       VERTEX PHARMACEUTICALS INCORPORATED
                                (Name of Issuer)

                                  COMMON STOCK
                         (Title of Class of Securities)

                                                     92532F100
                                 (CUSIP Number)

                                February 1, 1999
             (Date of Event Which Requires Filing of this Statement)


Check the  appropriate box to designate the rule pursuant to which this Schedule
is filed:

       [x  ]   Rule 13d-1(b)
       [   ]   Rule 13d-1(c)
       [   ]   Rule 13d-1(d)


*The  remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act') or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).


(1)     Names of Reporting Persons
       I.R.S. Identification Nos. of Above Persons (Entities Only)

       Robert C. Krembil

(2) Check the Appropriate Box if a Member of a Group

       (a)
       (b)        (x)

(3)    SEC Use Only


(4)    Citizenship or Place of Organization

       Robert C. Krembil is a citizen of Canada







Number of     (5)      Sole Voting Power                  37,200 shares
Shares
Benefici-     (6)      Shared Voting Power                     NIL
ally Owned
by Each       (7)      Sole Dispositive Power             37,200 shares
Reporting
Person With   (8)      Shared Dispositive Power               NIL


(9)    Aggregate Amount Beneficially Owned by Each Reporting Person

                           37,200 shares

(10)   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
                                                                 [   ]
                           Not applicable

(11)   Percent of Class Represented by Amount in Row 9

                           0.1 % of outstanding common shares

(12)   Type of Reporting Person             HC  (see item 2A)









                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 6)*


                       VERTEX PHARMACEUTICALS INCORPORATED
                                (Name of Issuer)

                                  COMMON STOCK
                         (Title of Class of Securities)

                                                     92532F100
                                 (CUSIP Number)

                                February 1, 1999
             (Date of Event Which Requires Filing of this Statement)


Check the  appropriate box to designate the rule pursuant to which this Schedule
is filed:

       [x  ]   Rule 13d-1(b)
       [   ]   Rule 13d-1(c)
       [   ]   Rule 13d-1(d)


*The  remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act') or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).


(2)     Names of Reporting Persons
       I.R.S. Identification Nos. of Above Persons (Entities Only)

       Arthur S. Labatt

(2)    Check the Appropriate Box if a Member of a Group

       (a)
       (b)        (x)

(3)    SEC Use Only


(4)    Citizenship or Place of Organization

       Arthur S. Labatt is a citizen of Canada







Number of    (5)      Sole Voting Power                  10,000 shares
Shares
Benefici-    (6)      Shared Voting Power                    NIL
ally Owned
by Each      (7)      Sole Dispositive Power             10,000 shares
Reporting
Person With  (8)      Shared Dispositive Power               NIL


(9)    Aggregate Amount Beneficially Owned by Each Reporting Person

                           10,000 shares

(10)   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
                                                                      [   ]
                           Not applicable

(11)   Percent of Class Represented by Amount in Row 9

                           0.0 % of outstanding common shares

(12)   Type of Reporting Person             HC  (see item 2A)









                                  UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                  SCHEDULE 13G
                    Under the Securities Exchange Act of 1934
                               (Amendment No. 6)*


                       VERTEX PHARMACEUTICALS INCORPORATED
                                (Name of Issuer)

                                  COMMON STOCK
                         (Title of Class of Securities)

                                                     92532F100
                                 (CUSIP Number)

                                February 1, 1999
             (Date of Event Which Requires Filing of this Statement)


Check the  appropriate box to designate the rule pursuant to which this Schedule
is filed:

       [x ]   Rule 13d-1(b)
       [   ]   Rule 13d-1(c)
       [   ]   Rule 13d-1(d)


*The  remainder of this cover page shall be filled out for a reporting  person's
initial filing on this form with respect to the subject class of securities, and
for  any  subsequent   amendment   containing   information  which  would  alter
disclosures provided in a prior cover page.

The information required in the remainder of this cover page shall not be deemed
to be "filed" for the purpose of Section 18 of the  Securities  Exchange  Act of
1934 ("Act') or otherwise  subject to the liabilities of that section of the Act
but  shall be  subject  to all other  provisions  of the Act  (however,  see the
Notes).


(3)     Names of Reporting Persons
       I.R.S. Identification Nos. of Above Persons (Entities Only)

       TRIMARK FINANCIAL CORPORATION

(2)    Check the Appropriate Box if a Member of a Group

       (a)
       (b)        (x)

(3)    SEC Use Only


(4)    Citizenship or Place of Organization

     Trimark  Financial  Corporation is a corporation under the laws of Ontario,
Canada







Number of    (5)      Sole Voting Power               2,507,300 shares
Shares
Benefici-    (6)      Shared Voting Power                NIL
ally Owned
by Each      (7)      Sole Dispositive Power          2,507,300 shares
Reporting
Person With  (8)      Shared Dispositive Power           NIL


(9)     Aggregate Amount Beneficially Owned by Each Reporting Person

                           2,507,300 shares

(10)   Check if the Aggregate Amount in Row (9) Excludes Certain Shares
                                                                        [   ]
                           Not applicable

(11)   Percent of Class Represented by Amount in Row 9

                           9.9 % of outstanding common shares

(12)   Type of Reporting Person             HC  (see item 2A)









                                    Item 1(a)

Name of Issuer:   VERTEX PHARMACEUTICALS INCORPORATED



                                    Item 1(b)

Address of Issuer's Principal Executive Offices:

130 Waverly Street
Cambridge, MA
02139



                                    Item 2(a)

Name of Person Filing:

Certain Trimark mutual funds (the "Funds"), which are trusts organized under the
laws of Ontario,  Canada, are owners of record of the securities covered by this
report.  Robert C. Krembil, a Canadian citizen,  and Chairman and shareholder of
Trimark Financial Corporation ("TFC"), and Arthur S. Labatt, a Canadian citizen,
and President and shareholder of Trimark Financial Corporation ("TFC"), are also
owners of record of a portion of the securities covered by this report.  Trimark
Investment  Management Inc. ("TIMI"), a corporation  incorporated under the laws
of Canada, is a manager and trustee of the Funds. TIMI is qualified to act as an
investment  adviser and manager of the Funds in the province of Ontario pursuant
to  a  registration  under  the  Securities  Act  (Ontario).  Trimark  Financial
Corporation  ("TFC") is a  corporation  incorporated  under the laws of Ontario,
Canada. It owns 100% of the voting equity securities of TIMI. Consequently,  TFC
may be deemed to be the beneficial owner of such securities.

                                    Item 2(b)

Address of Principal Business Office:

                            One First Canadian Place
                            Suite 5600, P.O. Box 487
                                Toronto, Ontario
                                     M5X 1E5

                                                   (416) 362-7181


                                    Item 2(c)

Citizenship:

     Robert C.  Krembil - Canada  Arthur S.  Labatt - Canada  Trimark  Financial
Corporation - Incorporated under the laws of Ontario,  Canada Trimark Investment
Management Inc. - Incorporated under the laws of Canada

       Trimark  mutual  funds - mutual fund trusts  organized  under the laws of
Ontario, Canada


                                    Item 2(d)

Title of Class of Securities:       common stock






                                    Item 2(e)

CUSIP Number:                       92532F100



                                     Item 3

If this  statement is filed pursuant to Rules 13d-1(b) or 13d-2(b) or (c), check
whether the person filing is a:

     (a) [ ] Broker or Dealer registered under Section 15 of the Act

     (b) [ ] Bank as defined in section 3(a) (6) of the Act

     (c) [ ] Insurance Company as defined in section 3(a)(19) of the Act

     (d) [ ] Investment  Company  registered  under section 8 of the  Investment
Company Act

     (e) [ ] An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E)

     (f) [ ] An employee  benefit plan or endowment fund in accordance with Rule
13d-1(b)(1)(ii)(F)

     (g) [ x] A parent holding company or control person in accordance with Rule
13d-1(b)(ii)(G)

     (h) [ ] A savings  association  as defined in Section  3(b) of the  Federal
Deposit Insurance Act

     (i) [ ] A church plan that is excluded from the definition of an investment
company under Section 3(c)(14) of the Investment Company Act

     (j) [ ] Group, in accordance with Rule 13d-1(b)(1)(ii)(J)

If this statement is filed pursuant to Rule 13d-1(c), check this box.   [   ]

                                     Item 4

Ownership.

       (a)      Amount Beneficially Owned:

                            2,554,500 shares

       (b)      Percent of Class:

                            10.1    %







       (c) Number of shares as to which such person has:

     (i) Sole power to vote or to direct the vote: 2,554,500

     (ii) Shared power to vote or to direct the vote: NIL

     (iii) Sole power to dispose or to direct the disposition of:2,554,500

     (iv) Shared power to dispose or to direct the disposition of:NIL






                                     Item 5

Ownership of Five Percent or Less of a Class

       [   ]    Inapplicable



                                     Item 6

Ownership of More than Five Percent on Behalf of Another Person

                Inapplicable


                                     Item 7

Identification  and Classification of the Subsidiary which Acquired the Security
Being Reported on By the Parent Holding Company.

                See item 2(a)


                                     Item 8

Identification and Classification of Members of the Group.

                Inapplicable


                                     Item 9

Notice of Dissolution of Group.

                Inapplicable









                                     Item 10

Certification.

       By signing  below I certify that, to the best of my knowledge and belief,
the  securities  referred  to above were not  acquired  and are not held for the
purpose of or with the effect of  changing  or  influencing  the  control of the
issuer of the  securities  and were not acquired and are not held in  connection
with or as a participant in any transaction having that purpose or effect.



Signature.

       After  reasonable  inquiry and to the best of my knowledge and belief,  I
certify that the information  set forth in this statement is true,  complete and
correct.



Date:                  February 1, 1999


Signature:             /S/ M. KEVIN FEENEY

Name/Title:            M. Kevin Feeney, Chief Financial Officer, on behalf of
                       Trimark Financial Corporation in its capacity as a
                       "Reporting Person" herein.


     Attention:  Intentional  misstatements  or  omissions  of  fact  constitute
Federal criminal violations (See 18 U.S.C. 1001).