The reference range of serum alanine amino transferase (ALT) for the local population was established by testing 5,000 random voluntary Chinese blood donors of various age groups of both sexes. In addition, 1,769 serum samples with elevated ALT levels were also collected for anti-HCV assays using both the Abbott and Ortho anti-hepatitis C virus (HCV) assay kits. The relationship between serum ALT and anti-HCV tests was studied and the performances of both kits used were compared. It was found that while the prevalence of serum anti-HCV was 0.4% among hepatitis B surface antigen-negative donors with normal ALT, subjects with ALT between 2 and 3 standard deviations (SD) and greater than 3 SD above the mean level had respective prevalence of anti-HCV 3 and 9.5 times that of the normal ALT subjects. Both anti-HCV kits were found to identify in majority the same positive population among the different groups of subjects studied. In addition, it was observed that for subjects who were anti-HCV-positive, the higher the serum ALT level, the higher the mean anti-HCV ELISA ratio and this observation was similar for both anti-HCV kits used. We conclude that: (1) there is a direct relationship between serum ALT level and anti-HCV positivity by EIA; (2) there is a direct correlation between serum ALT level and anti-HCV ELISA ratio, and (3) both Abbott and Ortho anti-HCV kits perform similarly in the identification of positive serum samples.