Four haemophiliacs with antibodies to factor VIII were treated on 7 occasions with fraction FEIBA. Satisfactory clinical results were achieved in patients receiving large doses of the preparation (63-105 units/kg). The administration of fraction FEIBA produced shortening of the whole blood clotting time but there was only a slight correction in the activated partial thromboplastin time. Two patients received prothrombin complex concentrate without clinical improvement in 1 case a good haemostatic effect was achieved after the infusion of cryoprecipitate and in 1 postoperative bleeding ceased with the administration of porcine factor VIII Immunosuppressive therapy with cyclophosphamide in 3 patients failed to prevent the anamnestic rise in antibody titer.