1.alpha.-Hydroxyvitamin D3 was prepared from cholesterol with a 1% overall yield. Hydroboration of 3.beta.-tetrahydropyranyloxycholest-5-ene followed by chromic acid oxidation and NaBH4 reduction gave 3.beta.-tetrahydropyranyloxy-5.alpha.-cholestan-6.beta.-ol. Brief treatment of its acetate with acid followed by Jones oxidation gave 6.beta.-acetoxy-5.alpha.-cholestan-3-one (7) in 55% yield from cholesterol. Introduction of C-1 double bond (64%) was effected by bromination of 7, followed by dehydrobromination with CaCO3, yielding 6.beta.-acetoxy-5.alpha.-cholest-1-en-3-one (9). Oxidation of 9 with alkaline H2O2 afforded the 1.alpha.,2.alpha.-epoxide (80%) and this was converted by 6 successive steps to 1.alpha.-hydroxycholesterol in 43% yield. The 5,7-diene cholesta-5,7-diene-1.alpha.,3.beta.-diol (19) was obtained from the acetate in 40% yield by allylic bromination with N-bromosuccinimide, dehydrobromination with trimethyl phosphite and saponification. UV irradiation of 19 in benzene solution followed by thermal isomerization produced 1.alpha.-hydroxyvitamin D3 (20%).