A total of 151 postmenopausal women were randomly allocated to 3 groups for treatment with hormone replacement therapy. One group received combined therapy (2 mg oestradiol (E2) and 1 mg norethisterone acetate (NETA) daily), the second group was placed on sequential therapy (2 mg E2 for 12 days, 2 mgE2 and 1 mg NETA for 10 days and 1 mg E2 for 6 days), while the third was given placebo. Treatment was administered over 24 cycles of 28 days. The two active treatments were equally effective in relieving climacteric symptoms. In the combined therapy group, 62% of the women experienced spotting and/or breakthrough bleeding during the first 3 cycles; thereafter this proportion decreased to between 3 and 18% in each of the following three-cycle periods. Sixty-four percent (64%) of these women had no more bleeding after the first 3 cycles. Endometrial atrophy was detected in 93% of the women in this group after 24 cycles of therapy. Bleeding irregularities occurred during the first 3 cycles in 27% of the patients treated with sequential therapy and in 21% of those receiving placebo. In the subsequent 3-cycle periods these figures fell to below 10% in the 2 groups. In all 3 groups weight remained stable but blood pressure increased equally in the actively treated groups and the placebo group. The levels of follicle-stimulating hormone (FSH), sex-hormone-binding globulin (SHBG) and the free fraction of E2 in serum were significantly lower in the combined therapy group than in the sequential therapy group. The higher level of free E2 in the latter group may have been caused by a decrease in metabolism associated with the increased SHBG concentration. It was concluded that combined treatment with E2 and NETA might provide an alternative to sequential treatment in postmenopausal women willing to tolerate the initial high risk of breakthrough bleeding/spotting in order to avoid subsequent regular bleeding. In the subgroup of women in whom bleeding irregularities continue, sequential treatment should be considered.