Hepatitis viruses A, B, C, D, and E have not accounted for all cases of hepatitis, hence "non A-E" agent(s) might be implicated. A set of new viruses (GBV-A, -B, and -C) whose genomes have been sequenced, are being investigated as possible causes of non A-E hepatitis. We investigated six cases of fulminant hepatitis of unknown aetiology for the presence of GBV-C genome in their serum, and three showed positive signals by semi-nested PCR using primers derived from the NS3/helicase region. Nucleotide sequence analyses confirmed these signals to be derived from a GBV-C sequence. The results suggest the importance of GBV-C in the aetiology of fulminant hepatitis.