Diagnosis of GB virus C (GBV-C) infection is based on RT-PCR methodology that detects genomic viral RNA. Four sets of primers located in different genomic regions were compared. These primers were used to amplify a reference panel of sera used by the French blood banks, including five positive sera, five negative sera and 10-fold serial dilutions of one positive serum. Three sets of primers located in the 5'UTR, NS3 and NS5a genomic regions gave comparable results with undiluted sera. When diluted sera were tested, the most sensitive protocol was that using a set of primers and a probe selected within the 5'UTR, together with a colorimetric detection based on DNA enzyme immunoassay.