Despite widespread clinical use of conjugated oestrogens, there is a paucity of reported studies concerning the effect of such therapy in sequential combination with the progestin, medrogestone (Colpro; Akromed). In a double-blind study, 22 oestrogen-deficient women who had undergone hysterectomy (mean age 52,8 years) were treated initially for 6 cycles with either conjugated equine oestrogens 0.625 mg (CEE) for 21 days plus a placebo during the last 10 days of each cycle or the same oestrogen regimen with 10 days of medrogestone 5 mg/d. Thereafter the treatments were crossed over for a further 6 cycles. CEE monotherapy resulted in significantly decreased levels of follicle-stimulating hormone (FSH), luteinising hormone (LH), prolactin (PRL) (P less than 0,001) and gamma-glutamyl transferase (P less than 0,01) with an increase in 17 beta-oestradiol (P less than 0,001). Medrogestone had a synergistic effect on the lowering of FSH, LH and PRL. No treatment modality caused any significant changes in blood pressure, fasting glucose value or vaginal cellular percentages. The decrease in hot flush scores, already manifest at the end of the first cycle, were sustained throughout (P less than 0,001).