RNA of a non-A to E hepatitis virus identified recently and designated provisionally GB virus C(GBV-C), was sought in patients in Indonesia by reverse-transcription polymerase chain reaction with nested primers deduced from a helicase-like region. GBV-C RNA was detected in 32 (55%) of 58 patients on maintenance hemodialysis at a frequency significantly higher (P < 0.001) than that in seven (5%) of 149 patients with chronic liver disease. Co-infection with hepatitis C virus was observed in 26 (81%) of the 32 patients on hemodialysis and in five (71%) of the seven patients with liver disease who were infected with GBV-C. Complete identity was observed in a sequence of 100 base pairs in the helicase-like region for GBV-C cDNA clones from some patients on maintenance hemodialysis. These results indicate that the patients on hemodialysis would be at high risk for GBV-C infection, which would be transmitted by transfusion and patient-to-patient routes.