Blood samples from 2000 accepted blood donors and 343 deferred donors with antibody to hepatitis B core antigen (anti-HBc) and/or an alanine aminotransferase (ALT) elevation were evaluated for antibody to hepatitis C virus (anti-HCV). Sixteen (0.8%) of the 2000 sera initially reacted on enzyme-linked immunosorbent assay (ELISA); 12 (0.6%) were repeatably reactive. One repeatably reactive sample had an elevated ALT; two reacted on anti-HBc testing and had ALT elevations. When the repeatably reactive ELISA samples were tested by an immunoblot assay, four reacted, three were indeterminate, and five did not react. Among the 343 deferred donors, HCV antibodies were detected in 8 (3.8%) of 210 anti-HBc-reactive samples, 12 (11.8%) of 104 elevated-ALT samples, and 15 (52%) of 29 combined elevated-ALT and anti-HBc-reactive samples; 25 of 28 reacted on immunoblot. The anti-HBc-reactive sera were subdivided into groups according to strength of anti-HBc reactivity (weak or strong) and antibody to hepatitis B surface antigen status and then were compared for anti-HCV reactivity rates. The group of samples showing the greatest frequency of anti-HCV had strong anti-HBc reactivity. For blood donors, the anti-HCV test correlates with the surrogate tests for non-A, non-B hepatitis (anti-HBc and ALT); however, most anti-HCV-reactive units remain undetected by surrogate tests, so that implementation of anti-HCV screening should further reduce the transmission of HCV via transfusion.