25 women aged 53--78 years with at least two years menopause were divided in three groups receiving one of the following oral treatments for three weeks: 2 mg oestradiol-17 beta plus 1 mg oestriol, 4 mg oestradiol-17 beta plus 2 mg oestriol or 50 micrograms ethinyloestradiol daily. Blood samples were collected before, during and after the treatment and the effect on the serum concentration of prolactin, oestradiol-17 beta, follicle-stimulating hormone and luteinizing hormonee was evaluated. During treatment with natural human oestrogens serum oestradiol-17 beta levels were significantly higher than before treatment. The serum concentration of prolactin was unchanged in patients receiving 2 mg oestradiol-17 beta plus 1 mg oestriol but increased in patients receiving 4 mg oestradiol-17 beta plus 2 mg oestriol or 50 micrograms ethinyl-oestradiol, thus indicating dose-dependence for natural human oestrogens. However, the increase was moderate, and these higher levels were not significantly different from levels of prolactin in serum found in 16 younger women. Concentrations of follicle-stimulating hormone and luteinizing hormon were depressed during treatment, the former to significantly lower levels when higher doses of oestrogens were used.