A population of 30 severe hemophilia-A patients with antibodies to factor VIII, treated with Autoplex since 1980, experienced a 30% incidence of non-A, non-B (NANB) hepatitis. 8 of the 9 patients affected had clinical signs of hepatitis and 7 had ALT levels in excess of 200 IU/l; the mean incubation time was 13 days. Only 5 of the 26 lots of Autoplex used were possibly transmitting the infective agent. An ELISA test to detect an antigen (DS-Ag) possibly related to NANB hepatitis was used to screen hemophilia-A and B patients. Its incidence was lower in patients treated less than 5 times a year (7.9%) than in patients treated over 15 times a year (25-27%) with locally prepared blood derivatives. Following treatment with Autoplex, the incidence of DS-Ag in inhibitor patients increased significantly (50%). In this last population, DS-Ag was shown to be unrelated to the NANB hepatitis observed. Although no direct evidence could be given, Autoplex was likely to transmit both the agent responsible for short incubation NANB hepatitis and DS-Ag.