A multicenter prospective study was carried out to evaluate whether a vapor-heated factor VIII concentrate transmitted blood-borne viral infections over a surveillance period of 15 months. Thirty-five patients with hemophilia and von Willebrand disease who had never received any blood components were treated. Twenty-eight were analyzed and found not to have non-A, non-B hepatitis. Sera from 20 of these 28 patients were also tested for the antibody to the hepatitis C virus. None had sero-converted during the follow-up period. None of the patients analyzed developed markers of the hepatitis B virus (n = 17) or the human immunodeficiency virus (n = 31). This vapor-heated factor VIII concentrate carries a low risk of transmitting hepatitis and human immunodeficiency virus infection.