The sera of 36 French patients with post-transfusional and sporadic non-A, non-B chronic hepatitis were investigated, for HBV and HCV infections using a combination of serological and polymerase chain reaction (PCR) assays. Anti-HCV was detected in 75% (27/36) of the patients by ELISA1 and/or RIBA2 tests. HCV-RNA sequences were found in 75% (27/36) of the sera by a single step PCR, using a set of primers located in the 5' non-coding region. Altogether, 89% (32/36) of the patients were found positive with serological and/or molecular tests. Among the positive patients, 68% (22/32) were found positive for both anti-HCV and HCV-RNA, 16% (5/32) and 16% (5/32) were found positive for either anti-HCV or HCV-RNA, respectively. HBV-DNA sequences were detected in two patients associated to the HCV viraemia. This study confirms the extremely high prevalence of HCV infection in NANB chronic hepatitis in France. It also shows possible co-infection by HCV and HBV in hepatitis.