1. Five normal subjects were given 100 ml of aluminium hydroxide gel per day for 28 days.
2. The phosphorus balance became more positive in one subject, less negative in two and changed from negative to positive in the other two subjects. This was accompanied by a rise in the concentration of the fasting morning plasma phosphorus. Calcium balance did not change.
3. The normal subjects absorbed 0·3–3·6 mmol of aluminium/day, which is significantly less than that absorbed by five patients with chronic renal failure, three of whom were studied before, and two after, the observations on the normal subjects had been completed.
4. In a further five normal subjects on 100 ml of aluminium hydroxide gel/day the 08.00 hours concentration of plasma phosphorus did not fall, though there was a fall at 11.00, 14.00 and 17.00 hours.