SECURED PROMISSORY NOTE


$434,361.95                   Deer Park, Texas                  March 15, 2002

      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 Thirty Four Thousand Three Hundred Sixty
One and 95/100  Dollars  ($434,361.95)  plus  interest  thereon at the rate of
Four and 52/100 percent (4.52%) per year 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 on March 14,  2008.  This Note shall also become due
and payable prior thereto to the extent that Maker  realizes any cash proceeds
from the sale or other  disposition  of the any of the shares of common  stock
of Payee which are pledged pursuant to the Pledge Agreement described below.

      The  principal  amount of this Note  represents  the  principal  of Four
Hundred  Eleven  Thousand  Four Hundred Two and 45/100  Dollars  ($411,402.45)
under that certain  Secured  Promissory Note dated February 9, 2001 from Maker
to Payee (the "Old Note") and all  accrued  thereon  through the date  hereof.
This Note is in full substitution and replacement of the Old Note.

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

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      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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