We studied the effects of physical activity and two types of estrogen treatment in a prospective study in 78 healthy postmenopausal women. A control group and two treatment groups receiving estradiol valerate and medroxy-progesterone acetate in 1- or 3-month cycles were monitored for 1 year. Half of each group took part in an exercise program. Lumbar and femoral bone mineral density increased in both of the estrogen-treatment groups. Physical exercise with estrogen treatment did not result in further increases in bone mineral densities.