Treatment of a patient with a severe inhibitor and consequent bleeding remained a problem. Management included protracted treatment with Factor VIII, use of immunosuppressive agents and prothrombin complex (or Factor IX) concentrates. The rationale for Factor IX was that it bypassed the defect in Factor VIII caused by the inhibitor. This method of therapy attracted wide popularity, but the success was greatly debated. It was intended at the very outset of the Factor VIII study that therapeutic trials involving patients with inhibitors would not be a prime function, but that such studies would be monitored if necessary. A controlled trial of Factor IX concentrates therapy was strongly advised by the DBDR Advisory Committee. Accordingly, during fiscal year 1978, a protocol for a double-blind control study was developed by the Factor VIII inhibitor group. The trial began in the spring of 1978, and the intervention terminated about one year later.