The influence of C-ring substituents on the biologic activity and protein binding properties of vitamin D3 has not been systematically investigated. To this end, cholesta-5,7-dien-3.beta.-ol was dehydrogenated to the 5,7,9(11)-triene. After protection of the 5,7-diene with a 4-phenyl-1,2,4-triazoline-3,5-dione Diels-Alder adduct, oxidation of the unprotected 9(11)-olefin gave epoxide 5. Reverse Diels-Alder and reductive ring opening of epoxide 5 gave cholesta-5,7-diene-3.beta.,11.alpha.-diol (6). Photolysis of 6 to the previtamin followed by thermal rearrangement resulted in 11.alpha.-hydroxyvitamin D3 (8). Vitamin 8 increased Ca transport at a dose of 500 pmol/rat but failed to increase bone Ca mobilization at a dose as high as 50,000 pmol/rat. Under the same conditions, corresponding doses of vitamin D3 and 25-hydroxyvitamin D3 increased bone Ca mobilization and intestinal Ca transport. The new vitamin analog, 8, was slightly less efficient (B-50 = 6.8 .times. 10-8 M) than 25-hydroxyvitamin D3, 24(R),25-dihydroxyvitamin D3 and 25(S),26-dihydroxyvitamin D3 (7.1 .times. 10-9 M, 7.7. .times. 10-9 M and 7.9 .times. 10-9 M, respectively) in displacing radiolabeled 25-hydroxyvitamin D3 from rat plasma vitamin D binding protein. Vitamin analog 8 showed significantly greater binding efficiency than 1.alpha.-hydroxyvitamin D3, 1,25-dihydroxyvitamin D3 and vitamin D3 (B-50 = 2.5 .times. 10-6 M, 9.84 .times. 10-8 M and 5.46 .times. 10-7 M, respectively), under these same conditions. Vitamin analog 8 displayed approximately the same efficiency as vitamin D3 in displacing radiolabeled 1,25-dihydroxyvitamin D3 from a chick intestinal cytosol receptor but was less effective than 25-hydroxyvitamin D3, 24(R),25-dihydroxyvitamin D3, 25(S),26-dihydroxyvitamin D3, 1.alpha.-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3. Introduction of an 11.alpha.-hydroxyl group into the C-ring of vitamin D3 results in a vitamin analog with moderate vitamin D3 agonist activity in the intestine but no activity with respect to bone Ca mobilization at the levels tested. 11.alpha.-Hydroxyvitamin D3 does not have improved binding affinity to the intestinal cytosol receptor when compared to vitamin D3. The new vitamin analog shows significantly greater binding affinity to plasma vitamin D binding protein than vitamin D3 (6.79 .times. 10-8 M vs. 5.46 .times. 10-7 M) or 1.alpha.-hydroxyvitamin D3 (6.79 .times. 10-8 M vs. 2.5 .times. 10-6 M), suggesting that the presence of an extra hydroxyl group sufficiently removed from the 3.beta.-hydroxyl is important in the binding of vitamin D analogs to vitamin D binding protein.