BACKGROUND & AIMS: For diagnosis of hepatitis C virus infection and monitoring of viral load in patients, a highly sensitive and accurate hepatitis C virus quantification system is essential. Methods: Hepatitis C virus genome was detected by real/time detection system using an ABI Prism 7700 sequence detector (Perkin Elmer Corp./Applied Biosystems, Foster City, CA). RESULTS: As few as 10 copies of the genome were detected, and the quantification range was between 10(1) and 10(8) copies (r > 0.99). This system was 10-100-fold more sensitive than an Amplicor monitor (Roche Diagnostic Systems, Branchburg, NJ). The coefficient of variation values for both intra-assay precision and interassay reproducibility of identifying the genome quantification ranged from 0.37% to 2.00% and 0.88% to 4.66%, respectively. The system could detect the genome in 98% of patients with chronic hepatitis, 95.8% of patients with liver cirrhosis, and 100% of patients with hepatocellular carcinoma who had the antibody to hepatitis C virus, but could not detect the genome in patients without the antibody. CONCLUSIONS: The establishment of a real-time detection system enables more accurate diagnosis of infection and monitoring of viral load in interferon-treated patients via quantification of viral genome.