Physiological dose of 1,25(OH)2D3 (0.03 microgram) normalized the phosphorus-calcium metabolism and improved the state of bone tissue in rats treated with hydrocortisone. An increased dose of 1,25(OH)2D3 (0.15 microgram) caused hyperphosphatemia and augmented osteoporotic alterations in the hydrocortisone-treated animals. 24,25(OH)2D3 at a dose of 0.3 mg did not exhibit any positive effect on phosphorus-calcium metabolism and on the state of bone tissue in rats with exogenous hypercorticoidism. At the same time, high doses of 24,25(OH)2D3 increased distinctly the bone tissue density as well as the content of calcium and phosphorus. The most favourable state of the calcium homeostasis and of bone tissue in exogenous hypercorticoidism was observed after simultaneous administration of 1,25(OH)2D3 and 24,25(OH)2D3. These data suggest that a set functionally active metabolites of vitamin D3 should be used in cases of long-term treatment with glucocorticoids.