AGREEMENT This will confirm the agreement by and among the undersigned that the Amendment No. 1 to Schedule 13D filed on the date hereof with respect to the beneficial ownership by the undersigned of shares of common stock, par value $.001 per share...

                                                                    EXHIBIT 99.1


                                    AGREEMENT


       This will confirm the agreement by and among the undersigned that the
Amendment No. 1 to Schedule 13D filed on the date hereof with respect to the
beneficial ownership by the undersigned of shares of common stock, par value
$.001 per share of SeraCare, Inc., a Delaware corporation, is being filed on
behalf of each of the undersigned in accordance with Rule 13d-1(k)(2) under the
Securities Exchange Act of 1934.

       IN WITNESS WHEREOF, the undersigned have executed this agreement as this
25th day of September, 2001.


                                      PROBITAS PHARMA, S.A.


                                      By: /s/ Xxxxxx Grifols Xxxxx
                                          ----------------------------------
                                          Xxxxxx Grifols Xxxxx
                                          Chief Executive Officer


                                      INSTITUTO GRIFOLS, S.A.


                                      By: /s/ Xx. Xxxxxx Xxxxx
                                          ----------------------------------
                                          Xx. Xxxxxx Xxxxx
                                          Chief Executive Officer


                                      SI MERGER CORP.


                                      By: /s/ Xxxxxx Grifols Xxxxx
                                          ----------------------------------
                                          Xxxxxx Grifols Xxxxx
                                          President