The consumption of moderately poisonous levels of toxic groundnut meal by turkey poults induced a degree of tolerance to aflatoxin Poults thus ;conditioned' gained more than ;unconditioned' birds on successively higher levels of aflatoxin and were enabled to survive and gain on rations which killed mature turkeys. Ingestion of aflatoxin led to marked alterations in the serum electrophoretic patterns followed in a few weeks by a return to nearly normal patterns. Subsequent increases in aflatoxin intake induced only minimal alternations in the serum patterns but the tolerance appeared unrelated to the hepatotoxic effect because extensive pathological changes developed in the liver.