1. The effect of a high calcium intake (1 mmol day−1 kg−1) alone or with the concomitant administration of oestradiol and testosterone derivatives was monitored by serial calcium balances in 48 patients with osteoporosis of various types.
2. On high calcium alone there was an increase (P < 0.001) in both total calcium balance and net calcium absorption as compared with values on a simulated home intake. This effect was sustained for periods up to 10 years (mean 3.5 years) by the addition of the hormones.
3. Discontinuation of the hormones (only) produced a significant decrease in both calcium balance and nett absorption but both were still increased when compared with the initial values under simulated home calcium intake.
4. No significant change in the urinary calcium output was observed under any of the regimens.