Plasma cortisol level in mastopathy and breast cancer patient was determined by radioimmunoassay, and influence of administered LH-RH on plasma cortisol level in breast cancer patient was studied. Cortisol level of postmenopausal patients with mastopathy was higher than that of premenopausals. Cortisol level was decreased by administration of LH-RH in premenopausal breast cancer patients, but postmenopausal group had variable plasma cortisol levels.