Effects of aflatoxin B1 and T-2 toxin, administered daily within 7 days at the doses of 0.7 mg/kg and 0.54 mg/kg, respectively, on metabolism of Ca and on the vitamin D hormonal system were studied in young rats kept on a ration containing normal (0.025 mg/kg) and high (0.25 mg/kg) amounts of vitamin D. Administration of the mycotoxins caused hypocalcemia, a decrease in absorption of Ca as well as in activity of alkaline phosphatase in small intestine mucose, while alterations in spongy bones (of the type of osteopetrosis) were most distinct in T-2 toxin treatment. Concentration of 25(OH)D3 in blood serum and activity of 25-hydroxylase D3 in liver tissue were decreased by 28% and 58%, respectively, after administration of T-2 toxin, and by 34% nd 33%, respectively, after treatment with aflatoxin B1. In kidney activity of I-hydroxylase 25(OH)D3 was unaltered and the activity of 24-hydroxylase tended to decrease. After treatment with the mycotoxins content of nuclear receptors of 1,25(OH)2D3 was decreased in small intestine mucose, whereas cytoplasmic receptors were increased 2.5-fold, thus indicating the distinct decrease in the receptors internalization. High doses of vitamin D caused an increase of Ca content in blood serum and of its absorption in small intestine as well as normalized Ca content in cortical bone of rats treated with T-2 toxin. At the same time, activity of 1-hydroxylase 26(OH)D3 was increased in liver tissue, while concentration of 1,25(OH)2D3 receptors was reduced in small intestine, but internalization of the hormone receptors was maintained at low level.(ABSTRACT TRUNCATED AT 250 WORDS)