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


                        SCHEDULE 13G


           UNDER THE SECURITIES EXCHANGE ACT of 1934
                  (AMENDMENT NO.  2    )*

                  Unilab Corporation
                     (NAME OF ISSUER)

               Common Stock, par value $.01 per share
                 (TITLE OF CLASS OF SECURITIES)

                      904763109
                    (CUSIP NUMBER)


Check the following box if a fee is being paid with this
statement |__|.  (A fee is not required only if the filing
person: (1) has a previous statement on file reporting beneficial
ownership of more than five percent of the class of securities
described in Item 1; and (2) has filed no amendment subsequent
thereto reporting beneficial ownership of five percent or less of
such class.) (See Rule 13d-7).

*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 the 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).


CUSIP NO. 904763109       13G          PAGE 2 OF 5 PAGES

1     NAME OF REPORTING PERSON
      S.S. or I.R.S. IDENTIFICATION NO. OF ABOVE PERSON
          Rockefeller & Co., Inc.
          I.R.S. Identification No.: 13-3006584

2    CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*
          Not applicable           (a)       |_|
                                   (b)       |_|

3    SEC USE ONLY

4    CITIZENSHIP OR PLACE OF ORGANIZATION
          New York

                    5      SOLE VOTING POWER
NUMBER OF                    3,591,504

SHARES              6      SHARED VOTING POWER
                              Not applicable.
BENEFICIALLY
                    7      SOLE DISPOSITIVE POWER
OWNED BY                      3,591,504

EACH REPORTING      8      SHARED DISPOSITIVE POWER
                              Not applicable.
PERSON WITH

9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
          3,591,504

10   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES
CERTAIN SHARES*
          Not applicable.

11   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW 9
          8.9%

12   TYPE OF REPORTING PERSON*
          IA

               *SEE INSTRUCTION BEFORE FILLING OUT!

                                     PAGE 3 of 5 PAGES

Item 1(a).  Name of Issuer:          

            Unilab Corporation

Item 1(b).  Address of Issuer's Principal Executive Offices:

            18448 Oxnard Street
            Tarzana, CA  91356

Item 2(a).  Name of Person Filing:

            Rockefeller & Co., Inc.

Item 2(b).  Address of Principal Business Office:

            30 Rockefeller Plaza, New York, New York 10112

Item 2(c).  Citizenship:

            New York

Item 2(d).  Title of Class of Securities:

           Common Stock, par value $.01 per share 

Item 2(e).  CUSIP Number:

            904763109

Item 3.     If this statement is filed pursuant to Rules 13d-
            1(b), or 13d-2(b), 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)  X      Investment Adviser registered under Section 203 of
            the Investment Advisers Act of 1940,

(f)         Employee Benefit Plan, Pension Fund which is subject
            to the provisions of the Employee Retirement Income 
            Security Act of 1974 or Endowment Fund;
            see 13d-(b)(1)(ii)(F),

(g)         Parent Holding Company, in accordance with 
            Rule 13d-1(b)(ii)(G),

(h)         Group, in accordance with Rule 13d-1(b)(1)(ii)(H).


                                       PAGE 4 of 5 PAGES



Item 4.     Ownership

            As of December 31, 1998:

       (a)  Amount Beneficially Owned:

            3,591,504

       (b)  Percent of Class:

            8.9%

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

           (i)  sole power to vote or to direct the vote 3,591,504,

           (ii) shared power to vote or to direct the vote -0-,

           (iii)sole power to dispose or to direct the
                disposition of 3,591,504,

           (iv) shared power to dispose or to direct the
                disposition of -0-.

Item 5.   Ownership of Five Percent or Less of a Class.

          Not Applicable.

Item 6.   Ownership of More than Five Percent on Behalf of
          Another Person.

          Rockefeller & Co., Inc. ("R&Co.") is making this filing
on behalf of certain clients for which it is the investment
manager (collectively, the "R&Co. clients").  Each of these R&Co.
clients, individually, owns less than 5% of this security.


                                       PAGE 5 of 5 PAGES

Each of these R&Co. clients has executed investment management
agreements granting R&Co. the right to exercise full discretion
with respect to all matters relating to the stock of the Issuer
held by them (including sole voting and dispositive power).
Thus, while R&Co. is for purposes of this filing regarded as the
beneficial owner of the shares of the Issuer held by each of the
R&Co. clients, each of the R&Co. clients has the sole right to
receive dividends from, and the proceeds from the sale of, the
securities of the Issuer owned of record by each of them.

Item 7.   Identification and Classification of the Subsidiary
          Which Acquired the Security Being Reported on By the Parent
          Holding Company.

          Not Applicable.

Item 8.   Identification and Classification of Members of the Group.

          Not Applicable.

Item 9.   Notice of Dissolution of Group.

          Not Applicable.

Item 10.  Certification.

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

February 12, 1998
(Date)

/S/David A. Strawbridge
(Signature)

David A. Strawbridge, Vice President
(Name/Title)