EXHIBIT 4.6

                        DEBENTURE SUBSCRIPTION AGREEMENT

         DEBENTURE  SUBSCRIPTION  AGREEMENT,  dated as of August 31,  2007 (this
"Agreement"), between First Banks, Inc., a Missouri corporation (the "Company"),
and First Bank  Statutory  Trust X, a statutory  trust created under the laws of
the State of Delaware (the "Trust"),  relating to the Junior  Subordinated  Debt
Securities  due  September  15,  2037 (the  "Junior  Subordinated  Debentures"),
issuable   pursuant  to  an  Indenture,   dated  as  of  August  31,  2007  (the
"Indenture"),  between the Company and LaSalle  Bank  National  Association,  as
Trustee. Capitalized terms used herein and not otherwise defined herein have the
respective  meanings  ascribed  thereto in the  Purchase  Agreement  (as defined
below).

         WHEREAS,  the Company,  the Trust and the Purchaser  named therein have
entered into a Capital Securities Purchase Agreement, dated August 29, 2007 (the
"Purchase  Agreement"),  in  connection  with  the  issuance  and  sale of trust
preferred  securities  (liquidation amount of $1,000 per security) (the "Capital
Securities") by the Trust; and

         WHEREAS,  the  Company  and  the  Trust  have  entered  into  a  Common
Securities Subscription Agreement, dated August 31, 2007 (the "Common Securities
Subscription  Agreement"),  in  connection  with the issuance and sale of Common
Securities (liquidation amount of $1,000 per security) (the "Common Securities")
by the Trust; and

         WHEREAS,  in  connection  with the  Purchase  Agreement  and the Common
Securities  Subscription  Agreement  and the  issuance  and sale of the  Capital
Securities and Common Securities pursuant thereto, the Trust desires to purchase
from the  Company,  and the  Company  desires to sell to the  Trust,  all of the
Junior Subordinated Debentures.

         NOW,  THEREFORE,  in  consideration  of the foregoing  premises and the
conditions and  agreements  hereinafter  set forth,  the parties hereto agree as
follows:

         1.    The Trust  hereby  subscribes for and offers to purchase from the
Company,  and the Company hereby accepts such offer and agrees to issue and sell
to the Trust,  contemporaneous  with the  Closing  Date,  Fifteen  Million  Four
Hundred Sixty Four Thousand Dollars ($15,464,000)  aggregate principal amount of
Junior Subordinated Debentures, in consideration of the payment on or before the
date  hereof of  Fifteen  Million  Four  Hundred  Sixty  Four  Thousand  Dollars
($15,464,000) in immediately available funds.

         2.    The Company represents and warrants that the Junior  Subordinated
Debentures have been duly authorized and executed by the Company, and, when duly
authenticated and delivered to the Trust in accordance with the terms hereof and
the Indenture,  will constitute the valid and binding obligations of the Company
entitled to the benefits of the  Indenture,  enforceable  against the Company in
accordance with their terms,  except to the extent that enforcement  thereof may
be  limited  by  bankruptcy,  insolvency,  reorganization,  moratorium  or other
similar laws affecting  creditors' rights generally or by general  principles of
equity (regardless of whether considered in a proceeding in equity or at law).

         3.    This Agreement  shall be  deemed  to be a contract made under the
laws of the State of New York,  and for all  purposes  shall be governed by, and
construed in accordance  with,  the laws of the State of New York without regard
to conflict of law principles.

         4.    This  Agreement  may  be executed in any number of  counterparts,
each of which when so executed  shall be deemed to be an original,  but all such
counterparts shall together constitute but one and the same instrument.





         IN WITNESS  WHEREOF,  the parties  hereto  have  caused this  Debenture
Subscription Agreement to be duly executed as of the date first written above.

                                    First Banks, Inc.



                                    By:  /s/ Lisa K. Vansickle
                                       -----------------------------------------
                                    Name:    Lisa K. Vansickle
                                         ---------------------------------------
                                    Title:   SVP - Chief Financial Officer
                                          --------------------------------------


                                    First Bank Statutory Trust X


                                    By:  /s/ Peter D. Wimmer
                                       -----------------------------------------
                                    Name:    Peter D. Wimmer
                                    Title:   Administrator


                                    By:  /s/ Lisa K. Vansickle
                                       -----------------------------------------
                                    Name:    Lisa K. Vansickle
                                    Title:   Administrator