1α, 25-Dihydroxy-21-norvitamin D₃ (3) was synthesized from 1α-hydroxydehydroepiandrosterone (4). Certain biological properties of 3 were examined in comparison with those of 1α, 25-dihydroxyvitamin D₃ (1) and 1α, 25-dihydroxy-21-nor-20-oxavitamin D₃ (2) to evaluate the effect of the 21-methyl substituent on biological activities. The differentiation-inducing activity of 3 towards human myeloid leukemia cells was approximately one-fifth of that of 1, while in the binding affinity with chick intestinal cytosolic receptor, 3 was about one-tenth of that of 1. The rather weak effect of 3 on serum calcium levels in normal mice at a dosage of 500μg/kg (intravenous administration) indicates that the essential importance of the 21-methyl moiety may lie in its effect on the regulation of calcium metabolism.