A multiplex polymerase chain reaction (PCR) was applied to clinical samples for simultaneous detection of hepatitis C virus (HCV) and GBV-C/HGV genome. With both RNA viruses, the amplification was performed with primers of the 5' UTR region starting from the single viral RNA reverse transcripted (cDNA) with random hexanucleotide primer mix. GBV-C/HGV RNA was detected in plasma sample of seven out of 50 transfused patients (14%). The multiplex PCR demonstrated a sensitivity up to 7.8 x 10(2) copies/ml respectively for GBV-C/HGV and HCV RNA in plasma samples of 5/50 patients with GBV-C/HGV/HCV co-infection and in patients with HCV (27/50) or GBV-C/HGV infection alone (2/50).