1. The acid excretion of patients with sickle-cell anaemia has been studied.
2. There is a mild defect in urinary acidification and a decreased H+ excretion in response to ammonium chloride loading.
3. The acidification defect was not corrected by oral administration of a phosphate solution.
4. Infusion of a sodium sulphate solution in subjects who were avidly reabsorbing sodium produced equal degrees of urine acidification in patients and controls.
5. Studies on bicarbonate reabsorption were inconclusive.
6. We conclude that patients with sickle-cell anaemia have a mild form of incomplete distal renal tubular acidosis.