During a period of 2 years, bone mineral content (BMC) was measured regularly in patients undergoing regular dialysis treatment (RDT). Low BMC values were found to be correlated to long duration of uremia, raised alkaline phosphatase activity, hyperaluminemia, hypermagnesemia, hypophosphatemia and clinical osteodystrophy. High levels of BMC loss were found among patients with relatively high initial BMC levels and severely calciopenic patients actually gained bone density during the investigation. Serum alkaline phosphatase activity and serum immunoreactive parathyroid hormone (PTH) levels were positively related to bone loss. It is suggested that the low BMC among RDT patients is caused by a predialytic loss that is arrested by entrance into a dialysis programme. Investigations using BMC or total body calcium as a measure of therapeutic effect must take account of this. The role of hypermagnesemia and hyperaluminemia remains undefined. Patients with BMC reduced below ca. 80% of normal may be candidates for treatment with active vitamin D metabolites.