The value of serum transaminases (ST) in evaluating hepatitis B (HBV) and C (HCV) infection was studied in 217 hemodialysis (HD) patients and 804 normal controls. Mean serum aspartate aminotransferase (AST) was 22.3 (22.0-22.7) and 22.6 (21.6-23.6) IU/l or 0.371 (0.366-0.378) and 0.376 (0.36-0.393) mu kat/l in controls and HD patients, respectively (nonsignificant), while mean serum alanine aminotransferase (ALT) was 20.3 (19.9-20.7) and 16.3 (15.3-17.3) IU/l or 0.338 (0.331-0.345) and 0.271 (0.255-0.288) mu kat/l in these two groups (p < 0.001). However, both AST and ALT became significantly depressed in HD patients after adjusting for age, gender, HBV surface antigen (HBsAg) and anti-HCV. The usual practice of regarding AST and ALT as being 'abnormal' in evaluating viral hepatitis when they exceeded the upper reference range (40 and 46 IU/l or 0.666 and 0.766 mu kat/l in our laboratory) was then critically assessed by the receiver operating characteristic (ROC) curve. ROC analysis showed that ST was useless in detecting HBsAg, while the best cutoff point for detecting the presence of anti-HCV was 18 IU/l (0.3 mu kat/l) for AST and 16 IU/l (0.266 mu kat/l) for ALT in HD patients, respectively. These are considerably lower than the conventional criteria for an 'abnormal' ST. We conclude that ST are decreased in HD patients and that the cutoff value of ST for detecting HCV should be set at lower levels to enhance their diagnostic yield.