Sixteen post-menopausal women who had never previously received any hormonal treatment applied Oestrogel cream 1.5 mg/day percutaneously for 1 yr. Skin biopsies were taken from the abdomen and from the lateral aspect of the thigh at 0, 3, 6 and 12 mth, and the changes in skin collagen content were noted. The abdominal skin collagen content increased significantly (P less than 0.001) over the 1-yr treatment period. The thigh skin collagen content also increased, but did not reach significant levels. There was a strong correlation between the change in skin collagen content (in both the abdomen and the thigh) and the original skin collagen content, indicating that the change in collagen content in response to oestrogen therapy is dependent on the original level. There is no further increase once an 'optimum' skin collagen level has been reached.