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

                              SCHEDULE 13G

               Under the Securities Exchange Act of 1934
                            (Amendment No. 2)


                      PharmChem Laboratories, Inc.
                            (Name of Issuer)

                              Common Stock

- ---------------------------------------------------------------------------

                    (Title of Class of Securities)

                              717133102
                           (CUSIP Number)



Check the following box if a fee is being paid with the statement / /.  (A
fee is not required only if the reporting 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 disclosures provided in a prior cover page.

The information required on 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).



SEC 1746 (2-92)


SCHEDULE 13G

CUSIP No. 717133102                     Page 2 of 7 Pages

- ---------------------------------------------------------------------------
1  NAME OF REPORTING PERSON
SS OR IRS IDENTIFICATION NO. OF ABOVE PERSON

Palo Alto Investors
IRS No.:  94-3088699
- ---------------------------------------------------------------------------
2  CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP*(a)/  /  (b)/X/
- ---------------------------------------------------------------------------
3  SEC USE ONLY
- ---------------------------------------------------------------------------
4  CITIZENSHIP OR PLACE OF ORGANIZATION

     California
- ---------------------------------------------------------------------------
       NUMBER OF         5    SOLE VOTING POWER
        SHARES                -0-
     BENEFICIALLY        --------------------------------------------------
      OWNED BY           6    SHARED VOTING POWER
        EACH                  851,500
      REPORTING          --------------------------------------------------
       PERSON            7    SOLE DISPOSITIVE POWER
        WITH                  -0-
                         --------------------------------------------------
                         8    SHARED DISPOSITIVE POWER
                              851,500
- ---------------------------------------------------------------------------
9    AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
     851,500
- ---------------------------------------------------------------------------
12   CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES*
                                                                      / /
- ---------------------------------------------------------------------------
13   PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
     15.2%
- ---------------------------------------------------------------------------
14   TYPE OF REPORTING PERSON*
     IA
- ---------------------------------------------------------------------------
                         *SEE INSTRUCTIONS BEFORE FILLING OUT!

SCHEDULE 13G

CUSIP No. 717133102                     Page 3 of 7 Pages

ITEM 1.

     (a)  The name of the issuer is PharmChem Laboratories, Inc.
("PharmChem").

     (b)  The principal executive office of PharmChem is located at 1505-A
O'Brian Drive, Menlo Park, CA 94025.


ITEM 2.

     (a)  The name of the person filing this statement is Palo Alto Investors
("PAI").

     (b)  The principal business office of PAI is located at 431 Florence
Street, Suite 200, Palo Alto, CA 94301.

     (c)  PAI is a California corporation. 

     (d)  This statement relates to shares of Common Stock of PharmChem (the
"Stock").

     (e)  The CUSIP number of the Stock is 717133102.



                                   SCHEDULE 13G

CUSIP No. 717133102                     Page 4 of 7 Pages

ITEM 3.  IF THIS STATEMENT IS FILED PURSUANT TO RULE 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)  /XX/  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 section 240.13d-1(b)(1)(ii)(F).

     (g)  /  /  Parent Holding Company, in accordance with section 240.13d-
1(b)(1)(ii)(F)

     (h)  Group, in accordance with section 240.13d-1(b)(1)(ii)(H)

ITEM 4.  OWNERSHIP.

     (a)  PAI beneficially owns 851,500 shares of the Stock.

     (b)  PAI beneficially owns 15.2% of the Stock outstanding.

     (c)   (i)  PAI has the sole power to vote or to direct the vote of 0
shares of the Stock.

           (ii)  PAI has the shared power to vote or to direct the vote of
851,500 shares of the Stock.

           (iii) PAI has the sole power to dispose or to direct the
disposition of 0 shares of the Stock.

           (iv)  PAI has the shared power to dispose or to direct the
disposition of 851,500 shares of the Stock.

                              SCHEDULE 13G

CUSIP No. 717133102                                    Page 5 of 7 Pages


ITEM 5.  OWNERSHIP OF FIVE PERCENT OR LESS OF A CLASS

If this statement is being filed to report the fact that as of the date
hereof the reporting person has ceased to be the beneficial owner of more
than five percent of the class of securities, check the following /  /.

Instruction:  Dissolution of a group requires a response to this item.



                                   SCHEDULE 13G

CUSIP No. 717133102                     Page 6 of 7 Pages

ITEM. 6.  OWNERSHIP OF MORE THAN FIVE PERCENT ON BEHALF OF ANOTHER PERSON

PAI is a registered investment adviser whose clients have the right to
receive or the power to direct the receipt of dividends from, or the proceeds
from the sale of, the Stock.  The only individual client whose holdings of
the Stock are more than 5 percent of the class is Banner Partners, a
California limited partnership of which William C. Edwards and Alan R. Brudos
are the general partners.  Banner Partners has filed a Schedule 13D
reflecting its holdings of the Stock.


                              SCHEDULE 13G

CUSIP No. 717133102                                    Page 7 of 7 Pages


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 purposes or effect.

SIGNATURES

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

DATED:     February 13, 1997

Palo Alto Investors


By:  /s/ William L. Edwards
     William L. Edwards, President

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