The negative strand RNA of hepatitis C virus, supposed to be a replicative intermediate of the virus appears to indicate viral replication. In this study, we detected the negative strand RNA by using reverse transcription-polymerase chain reaction with RNase A digestion to degrade the remaining positive strand genomic sequence of the virus after complementary DNA (cDNA) synthesis. In vitro transcribed positive-stranded mutant RNA was not detected by this method. Sample sera and liver tissues of 16 patients with chronic hepatitis C virus infection (liver fibrosis, 1; chronic hepatitis, 13; liver cirrhosis, 2) were analysed for negative strand RNA of hepatitis C virus. The negative strand RNA sequence was detected in 15 (93%) of 16 liver tissues and in 11 (78%) of 14 sera. The study demonstrated that negative strand RNA of hepatitis C virus in serum and liver tissue could be specifically detected.