A decrease in lean body mass and increased fat characterize menopause, related to both aging and likely decreased hormone secretion. Estrogen/androgen (E/A) treatment not only relieves vasomotor symptoms in menopausal women but demonstrably reduces fat mass while increasing lean body mass. This 16-week, double-blind trial randomly assigned 40 postmenopausal women (mean age 57 years) to receive either esterified estrogen alone (Estratab) in a dose of 1.25 mg daily (E group) or E/A therapy in the form of esterified estrogen plus 2.5 mg daily of methyltestosterone. The 37 women completing the study all had received estrogen for 3 months or longer. A double-dummy design was used to blind the study medication. In addition to anthropometric measurements, bone density was measured by dual-energy x-ray densitometry at the spine, hip, and forearm. The same technique provided estimates of fat mass, percentage of fat tissue, and lean body mass of the trunk and extremities. Muscle strength was estimated by weight lifting. The two treatment groups were demographically comparable. E/A treatment increased lean body mass in the trunk and extremities significantly more than estrogen alone. Body fat percentage declined significantly in the E/A group only. The difference between groups was significant for lean body mass and percentage of fat tissue when analyzing changes in the arms, legs, and trunk simultaneously. Body weight increased with E/A treatment by 2.7 pounds on average, and skin-fold thickness decreased. Upper- and lower-body strength increased with E/A treatment. Lower-body strength did not increase significantly with estrogen alone. Serum estradiol levels increased similarly in the two groups after 16 weeks. Percentage of free testosterone increased more in the E/A group, and luteinizing hormone and sex hormone-binding globulin values decreased significantly more in this group than in women given estrogen alone. Women given E/A therapy had significant reductions in total and high-density lipoprotein cholesterol and triglycerides, with no substantial change in low-density lipoprotein cholesterol. Low-density lipoprotein cholesterol fell significantly in the estrogen-only group. Several measures of sexual function demonstrated increases in frequency of sex, pleasure, and orgasms in women given E/A treatment. Changes were significantly more marked than in the estrogen group. Women in both groups exhibited an improved quality of life in several domains, including cognition, anxiety, depression, and vasomotor/sleep problems. Three women withdrew because of side effects, but no clinically significant liver dysfunction was observed. Postmenopausal women in good general health gained an improved body composition in this trial after 4 months of estrogen/androgen therapy. Muscle strength also improved, and these women seemed to have an improved quality of life and better sexual function compared with those given estrogen alone.