To investigate the influence of obesity on hormonal parameters in 186 apparently healthy women and in 176 women suffering from severe obesity the serum concentrations of FSH, LH, estrone (E1), estradiol (E2), androstenedione (A) and testosterone (T) were determined radioimmunologically. The climacteric onset of increased FSH production is 4 yr earlier (P less than 0.001) in obese than in normal women. Parallel to the rise of FSH there is a significantly premature decrease of the E1 and E2 concentrations in obese women. The typical elevation of the LH was found similar and not significantly different in the two collectives. The mean A levels are significantly lower (P less than 0.01) in obese than in normal women in all age groups. The T concentrations do not depend on the age of the women during the investigated period (41 to 60 yr) and are significantly higher (P less than 0.001) in the obese than in the normal women. There is a significant (P less than 0.001) correlation between the concentrations of A and E1 both in the obese and the normal women. An increased conversion of androgens to estrogens by adipose tissue is not revealed by the peripheral serum concentrations. Our data clearly demonstrate that in obese women the onset of ovarian insufficiency is significantly earlier than in normal women.