1. Eight patients with chronic renal failure (creatinine clearance 4·9–22·0 ml/min) were given 75–150 ml of aluminium hydroxide gel (‘Aludrox’) daily for 20–32 days.
2. In all patients there was a decrease in plasma phosphorus. The phosphorus balance became more negative in four and less positive in one, remained unchanged in two, and became positive in one.
3. Patients absorbed 100–568 mg of aluminium daily. In two of three patients the content of aluminium in the iliac bone increased but not above normal values.
4. The concentration of parathyroid hormone was decreased by aluminium hydroxide therapy in three patients in whom there was an increase in plasma calcium and in one other patient in whom plasma calcium did not change.