Various biochemical aspects of calcium metabolism were studied serially in 32 post-menopausal patients treated with subdermal implants of oestrogen, either alone or in combination with testosterone. Significant reductions in serum calcium, serum phosphate, the renal phosphate threshold (TmPO4) and the urinary calcium/creatinine ratio were observed for periods of up to 6 mth in both treatment groups as compared with baseline. The findings suggest that oestrogen replacement therapy by subdermal implant is effective in reversing the characteristic alterations in calcium metabolism which occur in the post-menopausal patient. The addition of testosterone does not appear to confer any additional benefit with respect to the parameters assessed.