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                                                                 EXHIBIT 10.23.1

                            SEROLOGICALS CORPORATION
                            780 PARK NORTH BOULEVARD
                                    SUITE 110
                            CLARKSTON, GEORGIA 30021

                                          April 18, 2000


Desmond H. O'Connell, Jr.
971 South Lagoon Lane
Mantoloking, New Jersey 08738

Dear Desmond:

                  Reference is hereby made to the letter agreement between you
and Serologicals Corporation (the "Corporation") dated November 12, 1999 (the
"Letter Agreement"). In consideration of your agreeing to continue to serve as
President and Chief Executive Officer of the Corporation on an interim basis at
the pleasure of the Board of Directors on the terms and conditions outlined in
the Letter Agreement (including but not limited to the per diem compensation and
the expense reimbursement), you are hereby granted Options to purchase
thirty-seven thousand five hundred (37,500) shares of the Corporation's common
stock ($.01 par value) at an initial exercise price equal to $4.6875 (the fair
market value as of the close of business on the date hereof). The Options shall
have a term of six (6) years. Twelve thousand five hundred (12,500) of the
Options shall vest on the date hereof and twelve thousand five hundred (12,500)
Options shall vest on each of May 10, 2000 and June 10, 2000, provided that you
are serving on the date of such vesting as President and Chief Executive Officer
of the Corporation; and provided, further, that in the event of the termination
of your employment for any reason (including the hiring of a permanent Chief
Executive Officer) prior to any vesting dates, any unvested Options shall
expire. Such Options shall be issued pursuant to a stock option agreement
entered into by you and the Corporation and shall be subject to all other terms
and conditions contained in the Corporation's Amended and Restated 1994 Omnibus
Incentive Plan, including a provision providing for acceleration of the vesting
of these Options upon "change in control".

                  This letter is to be governed by and interpreted in accordance
with the laws of the State of Georgia applicable to agreements made and to be
performed within that State except otherwise provided herein.

                  If any provision of this letter shall be determined to be
invalid, illegal or unenforceable in whole or in part, all other provisions
hereof shall remain in full force and effect to the fullest extent permitted by
law.
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                  The Corporation advises you that it is not providing legal
advice in connection with your acceptance and execution hereof and that, if you
so elect, you should consult with an attorney prior to such execution.

                  Please indicate your acceptance of this extension offer by
signing in the space provided below.

                                      Very truly yours,



                                       /s/ Lawrence E. Tilton
                                      ---------------------------------------
                                      Name:  Lawrence E. Tilton
                                      Title: Chairman, Compensation Committee

ACKNOWLEDGED AND AGREED:



 /s/ Desmond H. O'Connell, Jr.
-----------------------------------
Name: Desmond H. O'Connell, Jr.