Hydroboration of cholesta-1,5-diene-3-one followed by alkaline-peroxide oxidation resulted in the formation of 1α-and 2α-hydroxy derivatives of cholesterol in nearly equal-amounts. 1α-Hydroxycholesterol was then transformed to 1α-hydroxyvitamin D_3, via 1α-hydroxycholesta-5,7-diene-3β-ol (1α-hydroxyprovitamin D_3). 1α-Hydroxyvitamin D_3 was as active as 25-hydroxyvitamin D_3 in the stimulation of intestinal calcium transport and bone calcium mobilization in intact rats and moreover was able to produce both responses in anephric rats similar to 1α,25-dihydroxyvitamin D_3, the active metabolite of vitamin D_3, as reported originally by DeLuca's group.