Activity of aromatase (estrogen synthetase) was investigated in muscle tissue of 14 women and 2 men. The method of hard water release from androgenic precursor 3H-beta-androstendione was used. In men aromatase activity in muscle tissue is lower than women. For the latter group the enzyme activity is highest after 5-10 year of menopause and in the case of increased body fat content. In the future it looks interesting to correlate muscle tissue aromatase activity level with blood estrogens concentration, prevailing type of muscle fibers and physical activity rate of probands.