Polar glycosidic conjugates of vitamin D compounds occur in the vegetable and possibly in the animal kingdom. The biologic activity of these conjugates has not been examined systematically. To obtain more information on the biological role of such sterol conjugates, we examined the biological activity of the 3beta-D-glucopyranosyl conjugates of vitamin D3 5, 25-hydroxyvitamin D3 6, 1alpha-hydroxyvitamin D3 7 and 1alpha,25-dihydroxyvitamin D3 8. When these compounds were administered i.v. we found that a dose of between 50 and 500 pmol/rat of the four glucopyranosides tested increased active intestinal calcium transport and increased bone calcium mobilization in vitamin D-deficient rats fed a low calcium diet. Under the same conditions, corresponding doses of the parent vitamin D3 compounds elicited comparable increases in both intestinal calcium transport and bone calcium mobilization. When these compounds were administered p.o. 3beta-D-glucopyranosyl vitamin D3 5 exhibited no biological activity at doses of up to 5000 pmole/rat, whereas the corresponding glycosides of 25-hydroxyvitamin D3 6, 1alpha-hydroxyvitamin D3 7 and 1,25-dihydroxyvitamin D3 8 were active at doses of 500 to 1000 pmol/rat in the intestinal calcium transport system. When the glucopyranosyl conjugates were administered i.v. to vitamin D-deficient rats, 25-hydroxyvitamin D3 and 1alpha,-25-dihydroxyvitamin D3 were detected in the serum at levels less than or equal to those noted in animals dosed with the respective free sterols.