There are few reports regarding the effects of benzene and ethanol being administered simultaneously. In our experiments with 4 groups (controls, ethanol, benzene and ethanol plus benzene) Wistar male rats were treated with ethanol (20%) for 5 weeks, and then exposed to benzene (0.26 g/kg) for 5 days per week for 3 weeks. We also investigated the effects of benzene on the body weight, organ weight, peripheral hematology and hepatic drug metabolizing enzymes in the ethanol administrated rats. The liver weight increased significantly, but spleen weight decreased significantly in the benzene exposed group. Hematological examination showed a decrease of leukocyte in the two groups of benzene and ethanol plus benzene in comparison with the controls, but an effect promoted by ethanol was not found. Serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) values were not significantly different in the exposure groups when compared with the controls. The contents of microsomal cytochrome P450 in all the exposed groups showed a tendency to increase, but they were not significantly different in comparison with the controls. On the other hand, hepatic glutathione S-transferase activity in the exposed groups increased significantly.