Rats (Rattus norvegicus) were intraperitoneally injected with a 100 mg kg (-aEuro parts per thousand 1) dosage of benzene, a toxic and carcinogenic agent widely used for industrial purposes. Changes in lactate dehydrogenase (LDH), alkaline phosphatase (ALP), alanine amino transferase (ALT), aspartate amino transferase (AST) activities in serum of rats were investigated at 2, 4, 8, 16, 32, and 64 h following injection. Serum physiological was administered to control group. Activities were measured using autoanalyzer. Benzene caused significant activations in LDH, ALP, and AST activities in the serum at some test hours (p < 0.05). When compared with the control groups, although an increase occurred in ALT activity, it was seem that this increase wasn't significant (p > 0.05).