One of us (C.F.A.) has previously reported the successful use of one of the commercially available prothrombin complex concentrates for the control of bleeding episodes of haemophiltc patients with factor VIII inhibitors. Subsequent batches of these concentrates have not proved consistently effective even in doses of 150 factor IX units/kg every 24 hours. Recently an investigational preparation, Auto Factor IX, has been made available to us. This has a stated factor VIII correctional unit assay for each batch, (based on the ability to correct the prolonged APTT of plasma containing an inhibitor of factor VIII). We used 60-120 units/kg as an IV dose every 12 or 24 hours in the treatment of 24 bleeding episodes in 8 patients with factor VIII Inhibitor. The bleeding episodes were haemarthrosis (12) soft-tissue (6) intralingual (2) lacerations (2) retroperitoneal (1) and epidural (1). Rapid easing of pain and reduction of swelling was noted in all joints and soft tissue bleeds. In the retroperitoneal bleed cessation of bleeding was demonstrated by Technetium 99 Sulfur-colloid flow study, in the patient with epidural bleeding the hematoma was shown to reduce by serial CAT scans. Response was as good as we have come to expect from similar levels of factor VIII concentrate given to patients without an inhibitor. In 23 of the 24 episodes there was a marked reduction of APTT 10 minutes after the completion of the infusion.