Further studies of a patient with resistant osteomalacia have been presented. Balance studies have been performed in conjunction with tetracycline labeling of bone. Possible defects in intestinal calcium absorption, renal phosphate transport and the skeleton, and their respective roles in the pathogenesis of resistant osteomalacia, have been discussed. Important features in the patient described include normal parathyroid anatomy; an intestinal mucosa with the potential for absorbing calcium without the need for large doses of vitamin D; biopsy specimens of bone which were diagnostic of osteomalacia and consistent with severe inhibition of new bone formation and cellular proliferation; and decreased renal tubular phosphate transport. A pathogenetic mechanism involving combined defects consisting of impaired renal phosphate transport and an intracellular derangement at the skeletal level is proposed for this patient. It is suggested that resistant osteomalacia is a syndrome resulting from a variety of metabolic abnormalities.