The acute effects of Aflatoxin B I(AFB1) were evaluated on C57B 1/6, CBA/J, B 10A and Balb/c mice challenged with a single intraperitoneal dose of the mycotoxin (60 mg/Kg animal weight). 90 mice per strain were divided into three groups of 30 animals each: the intoxicated group and control groups I and II. Intoxicated mice were injected intraperitonealy with AFB1 dissolved in corn oil, while control I mice received corn oil only (0.01 ml/g) by the same route. Lots of l0 animals from the intoxicated and control groups were sacrificed 24, 72 and 168 hours after challenge. Control mice II remained untreated and were used as standards of normality for biochemical (hepatic and renal function) and hematological evaluation. AFB1 was detected in the liver of C57B 1/6 and CBA/J mice 24 hours (1.46 and 0.75 ng/g, respectively), 72 hours (2.30 and 0.08 ng/g, respectively), and 168 hours (2.18 and 0.25 ng/g, respectively) after challenge. The mycotoxin was also observed in the liver of B 10A mice (6.20 ng/g) 72 hours post-injection. The most evident histological lesions were observed 168 hours after treatment in C57B 1/6 and B 10A mice. Serum levels of alkaline phosphatase in intoxicated C57B 1/6 and B 10A mice were significantly higher than those of control I and II animals. The histopathologic lesions and biochemical changes were very discrete in Balb/c and CBA/J mice. It is included that strains C57B1/6 and B 10A are more susceptible than strains CBA/J and Balb/c to the acute effects ofAFB1. Such difference probably reflects each strains's ability to biotransform and eliminate AFB1 and its metabolites.