Administration of Prednisolone® (1-dehydrocortisol) to rats results in increased concentrations of 1,25-dihydroxycholecalciferol in serum. In spite of normal levels of this metabolite of vitamin D in the intestinal mucosa, the intestinal transport of calcium is inhibited in the Prednisolone®-treated animals. (Endocrinology 93: 718, 1973)