BACKGROUND: The efficiency of RNA isolation method is one of the important factors in hepatitis C virus (HCV) reverse transcription-polymerase chain reaction (RT-PCR) optimization. The standard methods for RNA isolation are laborious, time-consuming, and impractical for routine use in clinical laboratories. Commercial kits for RNA isolation are in common use but the studies for the efficiencies of each kits are rare in Korea. So we compared three simple commercial kits for RNA isolation (High Pure Viral RNA kit, RNAzol B kit and PrepMate l kit) for the recovery of HCV RNA from serum samples submitted for HCV RT-PCR. METHODS: We compared the results of 35 clinical samples submitted for HCV RT-PCR to assess the efficiency of RNA extraction of each kits. HCV RNAs were extracted from 35 serum samples by 3 commercial kits respectively. We performed HCV RT-PCR to compare the positive rates of HCV RNA from the samples extracted by each kits. Serial 10 fold-dilutions of positive control serum containing HCV RNA were made in 0.1% diethyl pyrocarbonate (DEPC) water and those diluted sera were used for extraction of HCV RNA by 3 commercial kits. We performed HCV RT-PCR with the diluted end points of the serially diluted positive control sera obtained by each kits. RESULT: The positive rates of HCV RT-PCR of 35 clinical samples of which RNA were extracted by 3 kits were 51.4% by High pure viral RNA kit, 45.7% by RNA PrepMate 1 kit and 40.0% by RNAzol B kit. The dilution end points of the serially diluted positive control sera were 10(-5) by High pure viral RNA kit, 10(-3) by RNAzol B kit and 10(-2) by RNA PrepMate I respectively. CONCLUSION: There were differences in the detection limits and positive rates of HCV RT-PCR among 3 RNA extraction kits. High Pure Viral RNA kit was more effective in HCV RNA extraction than RNAzol B and RNA PreMate I kit.