Two-hundred guinea pigs, weighing approximately 500 grams each, were placed in 8 groups, 4 of which received 20 micrograms/kg/day of partially purified aflatoxin for 7 days, followed by a 7 day recovery period. Paired groups then received 0, 20, 35 or 50 micrograms/kg/day of partially purified aflatoxin for 21 days. Animals were sacrificed periodically from all groups and blood was drawn for chemical and immunologic analysis. Weight gains were recorded and histopathologic studies were done on all animals. Pretreatment did not protect guinea pigs from a second exposure, and in fact enhanced mortality and liver toxicity as determined by histopathology. Serum chemistries and immunologic parameters of guinea pigs dosed twice were less conclusive, as neither high nor low doses differed from guinea pigs treated once. Glycocholic acid concentrations were more sensitive than traditional enzymes (aspartate and alanine amino transferase, alkaline phosphatase) for indicating hepatotoxicity.