Oral administration of retinyl palmitate to young Wistar rats during 7 days (70,000 IU of vitamin A per 100 g of body weight daily) caused a decrease in the liver UDP-glucuronosyl transferase and glutathione transferase activities and a significant decrease in the liver glutathione-SH content. A single administration of T-2 toxin (3 mg per kg of body weight) to rats after the treatment with high doses of vitamin A was accompanied by an increase in T-2 toxicity. The rat mortality was doubled and the decrease in UDP-glucuronosyl transferase and glutathione transferase activities was more distinct as compared with the rats treated with T-2 toxin only. Vitamin A excess appears to decrease the phase II drug-metabolizing enzyme activities and glutathione-SH content in rat liver tissue. Excess of vitamin A may be responsible for an increase of T-2 toxicity in rats.