Various aspects of calcium and bone metabolism were studied in 50 cases of chronic renal failure. It was found that elevation of plasma alkaline phosphatase was generally associated with reduced metacarpal cortical thickness and in a small number of biopsies reflected the osteomalacic rather than the resorptive component of renal bone disease. Patients with an elevated plasma alkaline phosphatase tended to have a lower plasma calcium, lower plasma bicarbonate and lower radiocalcium absorption than patients with a normal alkaline phosphatase. Hypocalcaemia was frequently associated with, and attributed by the authors to reduced tubular reabsorption of calcium, which in turn appeared to be related to the degree of metabolic acidosis. The authors conclude that metabolic acidosis predisposes to hypocalcaemia and, therefore, to renal osteomalacia.