This prospective study was carried out with the aim of evaluating the efficacy of solvent/detergent inactivation of the hepatitis C virus (HCV) as applied to a chromatographic factor VIII concentrate. In parallel, the markers for other viruses, either lipid-enveloped (human immunodeficiency virus types 1 and 2 [HIV-1 and -2] and hepatitis B virus [HBV]) or non-lipid-enveloped viruses (such as B19 parvovirus and hepatitis A virus [HAV]) were evaluated. The study included 14 hemophilia centers, which enrolled 36 previously untreated patients (median age, 3 years; range, 1-56). The length of follow-up was 12 months, during which HCV (first- and second-generation assays and recombinant immunoblot assay), HIV-1 and -2, HBV, HAV (IgG and IgM), and parvovirus (IgG and IgM) antibodies, as well as alanine aminotransferase values were evaluated. Thirty-one patients were analyzable; none seroconverted for HCV, HBV, or HIV after exposure to a total of 165,000 IU of factor VIII (41 different lots). In one patient, alanine aminotransferase values rose to 167 mU per mL, 6 weeks after the first concentrate infusion, and this patient seroconverted for HAV 1 week later. Furthermore, 10 patients seroconverted for parvovirus during follow-up. This study suggests that the solvent/detergent method of virus inactivation is efficient in relation to lipid-enveloped blood-borne viruses but not in relation to non-lipid-enveloped viruses.