The synthesis of long cDNA molecules encoding the complete genome of RNA viruses has recently been demonstrated; this major improvement has numerous practical applications such as construction of infectious cDNA clones or study of sequence variability at the level of a single RNA molecule. Using hepatitis C virus (HCV) as a model, we established an RT-PCR technique for amplification of cDNA fragments with a length of about 5 kb. The RT reaction was carried out with a Moloney murine leukaemia virus reverse transcriptase lacking detectable RNase H activity. For PCR reactions an enzyme mix containing Taq and Pwo DNA polymerases was used. Hot start and addition of 5% DMSO were also important to efficiently achieve long PCR products. About 10(6) HCV genome equivalents/ml in serum were needed in order to amplify the HCV genome in only two cDNA fragments covering about 98% of the complete genome. Analysis of the HCV quasi-species is also possible by this method as shown by sequencing of the hypervariable region 1 (HVR1) after cloning of cDNAs. The integrity of the long cDNA clones was proven by (1) restriction analyses, (2) partial sequencing and (3) expression of respective gene products. In vitro transcribed cDNAs were translated in rabbit reticulocyte lysate. Structural and nonstructural HCV proteins were identified by immunoprecipitation using patient serum. These results suggest that the two cDNA clones encode a complete and functional open reading frame of HCV.