The role of vitamin D in hepatic osteodystrophy was examined. Eleven unselected patients with primary biliary cirrhosis (PBC) were assessed for disorders of mineral and vitamin D metabolism. Six were not receiving supplementary vitamin D, and five were being treated with oral vitamin D (50,000 IU daily). Serum levels of 25-hydroxyvitamin D were normal in all patients receiving oral therapy and in 4 of 6 untreated patients. Levels of serum 1,25-dihydroxy vitamin D and 24,25-dihydroxyvitamin D were normal or near normal in all patients. Studies were repeated after 6 months of therapy with parenteral vitamin D2 (100,000 IU i.m. monthly) in 7 patients. Initial bone histomorphometry revealed no evidence of osteomalacia or osteoporosis. However, the bone resorption surface of trabecular bone was increased. This abnormality was no longer present on repeat bone biopsies obtained after parenteral vitamin D therapy, and bone formation had decreased. In addition, trabecular bone volume remained normal in the face of the lower rate of bone formation. Increased bone resorption surface in the absence of osteoporosis or osteomalacia has not been previously described in PBC. Improvement in this bone parameter, associated with the finding of a decrease in the formation of bone and in hydroxyproline excretion in urine after parenteral vitamin D, suggests that increased turnover may be an early feature of the bone disease which complicates PBC and that parenteral vitamin D may retard the rate at which hepatic osteodystrophy develops in chronic cholestatic liver disease.