In the present study, an investigation was undertaken to assess the efficacy on serum enzymes of colloidal bismuth subcitrate (CBS). CBS was administered with injections to male rats in 100-, 200-, 400-, 500-, and 1000-mu g/L doses of bismuth. Rats were anesthetized at different intervals (24, 48, and 72 h) after CBS injections. The levels of serum enzymes were determined. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and creatine kinase (CK) levels significantly increased after all CBS treatments without dependence on time. All doses of bismuth significantly affected the lactate dehydrogenase (LDH) in serum after 72 h. The lowest doses were the most toxic on ALT and LDH. These data suggest that treatment with CBS can provide evidence for a possible marker of liver toxicity although there is no evidence of liver accumulation of bismuth in the present study.