SummaryThe present study compares two new factor VIII preparations currently used in the treatment of haemophilia A. Factor VIII was partially purified from plasma obtained from unpaid voluntary Belgian donors in the blood transfusion centers of Lille and Amsterdam and virus-inactivated by exposure to solvent-detergent (FVI1I-SD) or by pasteurization (FVIII-P) respectively.The factor VIII content and the purity of both preparations were assessed in vitro, wheras in vivo we studied the recovery and the plasma half-life of both concentrates. The higher purity of FVIII-SD was confirmed. Factor VIII-P preparations contained more factor VIII than mentioned on the label. Both preparations gave good in vivo recoveries and half-lives. Patients who did not have antibodies to hepatitis B, hepatitis C or HI V at the initial screening, remained negative after six months treatment with the new concentrates. No patients developed neutralizing factor VIII antibodies. Furthermore patients appreciated the ease of administration of both preparations. In conclusion both FVIII concentrates are suited for the treatment of hamophelia A patients.