SECURED PROMISSORY NOTE


$411,402.45                      Deer Park, Texas              February 9, 2001


        FOR VALUE RECEIVED,  B. Tom Carter, Jr. ("Maker") hereby promises to pay
to the order of HydroChem Holding, Inc., a Delaware corporation  ("Payee"),  the
principal  amount of Four Hundred  Eleven  Thousand  Four Hundred Two and 45/100
Dollars  ($411,402.45)  plus  interest  thereon  at the rate of Five and  07/100
percent (5.07%)  compounded  annually,  and payable as provided herein in lawful
money of the United  States of America,  at Deer Park,  Texas,  or at such other
place as Payee of this Note may from time to time designate by written notice to
Maker.

        The principal amount of this Note and all accrued interest thereon shall
be due and payable  upon the earlier of February 8, 2007 or any  termination  of
Maker's employment with the Payee or Payee's wholly-owned subsidiary,  HydroChem
Industrial Services, Inc., but not earlier than February 8, 2004.

        Of the principal  amount of this Note,  Fourteen  Thousand Eight Hundred
Seventy  Five and 00/100  Dollars  ($14,875.00)  are in full payment for certain
shares of the Payee's Class A Common Stock being acquired by the Maker as of the
date hereof  pursuant to the  exercise of two stock  options each at an exercise
price of One Dollar ($1.00) per share. The balance of the principal represents a
substitution  and replacement of Maker's  Secured  Promissory  Notes  (including
accrued interest  thereon) dated April 30, 1999 and May 15, 2000,  respectively,
to Payee.

        Pursuant to a Pledge  Agreement of even date herewith  between Maker and
Payee, and as more specifically  described therein,  this Note is secured by the
pledge of certain  shares of common stock of Payee which are owned  beneficially
and of record by Maker,  and which  include,  but are not limited to, the shares
being  acquired  by the  Maker  pursuant  to  the  aforementioned  stock  option
exercises.

        This Note may be prepaid in whole or in part without premium or penalty.

        If this Note is placed in the hands of an attorney for collection  after
default, or if all or any part of the indebtedness represented hereby is proved,
established or collected in any court or in any bankruptcy, receivership, debtor
relief, probate or other court proceedings,  then Maker agrees to pay reasonable
attorneys'  fees and collection  costs to Payee in addition to the principal and
interest payable hereunder.

        If default is made in the payment of the  principal  or  interest  under
this Note,  or if a default  occurs  under any other  instrument  evidencing  or
securing  payment  hereof,  then in any  one or more  such  events,  the  entire
principal balance and accrued interest owing hereon shall at once become due and
payable,  at the option of Payee.  Failure to  exercise  this  option  shall not

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constitute  a waiver  of the  right  to  exercise  the same in the  event of any
subsequent default.

        Maker,  signers,  sureties,  and endorsers of this Note severally  waive
notice of  acceleration  of maturity if such shall occur,  demand,  presentment,
notice of dishonor,  diligence in  collecting,  grace,  notice and protest,  and
agree to one or more  extensions  for any period or periods of time and  partial
payments, before or after maturity, without prejudice to Payee.

        THIS NOTE SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS
OF THE STATE OF TEXAS.


                                     MAKER:


                                                   /s/ B. Tom Carter, Jr.
                                                   ----------------------
                                                   B. Tom Carter, Jr.
                                                   5956 Sherry Lane
                                                   Suite #930
                                                   Dallas, Texas  75225



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