To assess the prevalence of hepatitis C virus (HCV) infection in the pregnant women in Taiwan, we investigated two groups of pregnant women, 944 women without serum alanine aminotransferase (ALT) screening (group A) and 197 women with abnormal ALT (greater than 45 IU/L) (group B). They were checked for anti-HCV (anti-C100-3) with HCV EIA kit (Abbott Lab., North Chicago, IL). The results showed that 21 (2.2%) in group A and 5 (2.5%) in group B were anti-HCV-positive. However, 15 out of 21 in group A had an optical density (O.D.) of anti-HCV less than 1.0, were negative by recombinant immunoblot assay (RIBA), and were regarded as false-positive. Nine infants delivered by those 11 cases were negative for anti-HCV at 6 months of age, while none of the 8 husbands were anti-HCV-positive. It is concluded that the prevalence of anti-HCV in pregnant women in Taiwan is low (6/944, 0.63%), even in the cases with abnormal ALT (5/197, 2.5%). There was no serologic evidence for perinatal transmission or spouse infection.