Many clinical manifestations shown by obese women point to the disturbances of secretory activity of hypothalamus-pituitary-ovary axis (h-p-o). Because of antigonadotropic activity of melatonin (MEL) it is essential to define this hormone participation in inducing the disturbances of the h-p-o axis. We evaluated the relationship between MEL secretion and circadian concentrations of LH, FSH, E[_2], P, TT, FT, SHBG as measured at 3 h intervals, in 9 obese women showing android type of adipose tissue distribution (BMI > 30 kg/m[^2]; WHR > 0.8) and in 6 women showing gynoid type of adipose tissue distribution (BMI > 30 kg/m[^2]; WHR < 0.8). All patients were between 55 and 62 years of age. A considerable increase of circadian MEL secretion was observed in all obese patients. Suppression of MEL rhythmicity was observed in all patients, while nocturnal phase shift of MEL occurred only in women showing android type of adipose tissue distribution. Significant decrease of circadian LH, P and SHBG values which was accompanied by the elevation of E[_2], TT and FT levels was observed in women with a disturbed rhythmicity of MEL secretion (particularly in case of androidal-type obesity). Based on these results it is suggested that MEL participates in inducing h-p-o axis disturbances in obese women of post-menopausal age.