EXHIBIT A

                 RELEVANT SUBSIDIARIES OF PARENT HOLDING COMPANY

PART A: TCW ENTITIES

PARENT HOLDING COMPANY:

       The TCW Group, Inc.

       Robert Day (an individual who may be deemed to control The TCW Group,
       Inc.)


RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13D-1(B):

(i)  Trust  Company of the West, a California corporation and a bank as  defined
     in Section 3(a)(6) of the Securities Exchange Act of 1934.

(ii) TCW  Asset  Management Company, a California corporation and an  Investment
     Adviser  registered  under Section 203 of the Investment  Advisers  Act  of
     1940.

(iii)      TCW  Investment Management Company, a California corporation  and  an
     Investment Adviser registered under Section 203 of the Investment  Advisers
     Act of 1940.

Note:     No Common Stock of Arena Pharmaceuticals, Inc. is held directly by The
     TCW Group, Inc. Other than the indirect holdings of The TCW Group, Inc., no
     Common  Stock of Arena Pharmaceuticals, Inc. is held directly or indirectly
     by  Robert  Day, an individual who may be deemed to control The TCW  Group,
     Inc.

PART B: NON TCW ENTITIES

PARENT HOLDING COMPANY:

        Robert Day (an individual who may be deemed to control the entities
        described below which are not subsidiaries of The TCW Group, Inc.)

RELEVANT SUBSIDIARIES THAT ARE PERSONS DESCRIBED IN RULE 13D-1(B):

        Oakmont Corporation, a California corporation and an Investment Adviser
        registered under Section 203 of the Investment Advisers Act of 1940.





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