Three sequential oestradiol valerate (E2V) and cyproterone acetate (CPA) combinations based on 11 days of oestrogen and 10 days of oestrogen-progestogen administration were investigated during hormone replacement therapy in two prospective, double-blind randomized trials. Treatment A comprised 2 mg E2V and 1 mg CPA, treatment B, 1 mg and 0.5 mg and treatment C, 2 mg and 2 mg, respectively. During treatment A hot flushes (P < 0.0001), night sweating (P < 0.0001), depression (P = 0.0001), dizziness (P = 0.0001) and insomnia (P = 0.003) decreased significantly. The only side effect was breast tenderness, which was experienced by 18% of the women. Weight and blood pressure, thyroid, adrenal, liver and kidney functions, parathyroid hormone and vitamin D, platelets and blood cell counts did not change during the 12 months of therapy. In the women who received treatment A the menstrual flow became less abundant during the early months of treatment (P < 0.0001), the menses being scanty in around 30% of the women, while some 10% had amenorrhoea. Spotting occurred in 10-20% of the subjects. Endometrial biopsies were atrophic in 10% of the women, whereas a normal secretory phase was observed in 45% and irregular secretion in 45%. After careful analysis using visual analog scales, these findings were interpreted as indicating a high-normal progestational effect. In comparison with the pattern observed in normal menstrual cycles the women who received treatment A had a more heterogenic glandular epithelium, with more papillae, larger stromal cells, a more pronounced decidual reaction and more fibrinoid material. No cases of hyperplasia were seen. Treatment B was less effective than treatment A in relieving climacteric complaints. Irregular bleeding was troublesome in over 20% of cases and amenorrhoea occurred in 50%. Endometrial biopsies were atrophic in 57% of the women. The effectiveness of treatment C in alleviating flushes, sweating, dizziness and depression was the same as that of treatment A. The decrease in menstrual flow during the early months and the incidence of amenorrhoea (approx. 10%) and atrophic endometria (approx. 10%) were comparable. Detailed analysis revealed that C had an even stronger progestational effect than A. It was concluded that A was the treatment of choice in comparison with B and C. It proved highly effective in treating climacteric complaints, had no side effects apart from breast tenderness, provided good cycle control and induced a physiological secretory transformation of the endometrium.(ABSTRACT TRUNCATED AT 400 WORDS)