Transdermal oestradiol, 100 micrograms/d, was used to treat 11 women suffering from postmenopausal symptoms. After 3 weeks therapy there was a significant rise in the plasma oestradiol into the premenopausal range and a significant fall in plasma FSH level and symptom score. Bone resorption, assessed by urinary excretion of calcium and hydroxyproline, decreased significantly while plasma alkaline phosphatase activity remained constant. There was a significant fall in plasma calcium and phosphate but the plasma concentrations of PTH, calcitonin and calcitriol and the urinary excretion of cAMP were unchanged. Plasma levels of vitamin D binding protein, albumin and globulin were unaltered, and blood pressure did not rise. These effects were similar to those found in postmenopausal women with oral ethinyloestradiol, 30 micrograms/d, (Selby et al., 1985), apart from those on plasma vitamin D binding protein, total calcitriol, albumin, globulin, tubular reabsorption of phosphate and blood pressure, changes which probably arise from a direct action of oral oestrogen on the liver.