The prevalence of antibody to hepatitis C virus among Chinese subjects in Taiwan was evaluated using a commercially available enzyme immunoassay. The overall prevalence of antibody to hepatitis C virus was 0.28% among 1,419 healthy subjects, 0.8% among 500 unselected paid blood donors and 0.4% among 793 pregnant women. The three offspring of the mothers positive for antibody to hepatitis C virus were all found to be positive for antibody to hepatitis C virus at birth but all became negative by the age of 6 mo. Among healthy subjects, none of 1,000 school children and young adolescents had antibody to hepatitis C virus. Among patients in selected "high-risk" groups, antibody to hepatitis C virus was detected in 100% of 9 hemophiliac patients who were positive for antibody to human immunodeficiency virus, in 53% of 115 intravenous drug abusers, in 34.4% of 96 hemodialysis patient and in 15.8% of 19 homosexual men who were positive for antibody to human immunodeficiency virus. Only 7.1% of 196 prostitutes, 5.9% of 34 spouses of patients positive for antibody to hepatitis C virus and 0.5% of 201 brothelgoers had antibody to hepatitis C virus. These findings suggest that hepatitis C virus is transmitted mainly by the parenteral route in Taiwan. Transmission from mother to infant is not an important mode of spread of hepatitis C virus.