The authors report two cases of vitamin resistant osteomalacia in an adult connected with an apparent inability of the liver to hydroxylate vitamin D. One of the cases showed a case of pseudo-hypo parathyroidism of type II, reversible by the administration of calcium. The other case demonstrated vertebral hyperossification. Treated with 25 hydroxycholecalciferol in physiological dosage an improvement in the clinical, biochemical and histological states resulted.