Of forty-three perimenopausal women aged 40.1-56.5 years with climacteric complaints 25 were treated with sodium piperazine estrone sulphate 2.5 mg daily and 18 were given methyl scopolamine. All subject had initial serum FSH levels in the postmenopausal range (20 U/l). The serum levels of FSH, LH, unconjugated immunoreactive estrogens, total estrone, total dehydroepiandrosterone (DHAS), and the urinary low polar estrogens were followed during 18 months of treatment. In the estrogen treated group serum unconjugated immunoreactive estrogens and total estrone as well as urinary low polar estrogens increased significantly during treatment. The serum levels of FSH decreased significantly during the whole test period; LH only at three months. No effects could be seen on serum DHAS. In the group given methyl scopolamine the only changes found were a decrease in FSH at three months and a positive trend for LH (during the whole treatment period). In the total material, positive correlations were found between pretreatment values of unconjugated immunoreactive estrogens and total estrone and between total estrone and DHAS. A negative correlation was found between unconjugated immunoreactive estrogens and FSH. It is concluded that the effects of estrogens on the endocrine system in peri- and postmenopausal women are influenced by chemical structure, dosage and mode of administration of the estrogen as well as by the endogenous hormone profile.