To identify areas endemic for hepatitis C virus (HCV), we attempted to predict the prevalence of antibody to HCV (anti-HCV) in a community by the prevalence of elevated levels of alanine aminotransferase (ALT). The results of health examinations of 2,273 women > or = 40 years old in five townships in central Taiwan were analyzed. The overall prevalence of elevated ALT levels was 11.6%. A township (20.3%) and 10 villages were identified as having a high prevalence (17.9-40.0%) of elevated ALT levels. Five communities with variant rates of elevated ALT levels, which ranged from 8.0% to 27.3%, were selected for correlation with the prevalence of anti-HCV among adults (> or = 40 years old). The prevalence of anti-HCV, which ranged from 10.1% to 72.1%, were obtained by community screenings and/or hospital-based studies. The correlation equation used was the prevalence of anti-HCV (%) = 3.33 x (prevalence of elevated ALT levels (%) - 5.7%) (r2 = 0.94, P < 0.01). Using this method, areas endemic for HCV can be identified by determining the community prevalence of elevated ALT levels.