Cardiovascular morbity and mortality and lower in menstruating and in posmenopausal woman receiving estrogen. In this investigation, we have studied the sympathetic response to standing during the follicular and luteal phases of the menstrual cycle. In 16 normal women, the baseline plasma norepinephrine levels in the follicular phase were 82.3 + o - 7.4 pg/ml and increased to 113. 0 + o - 6.3 pg/ml (p < 0.0001), during the luteal phase of the menstrual cycle. Estradiol levels were also higher in the luteal phase (118.1 + o - 7.6 pg/ml) compared to the follicular phase (4.8 + o - 5.0 pg/ml p < 0.0001). in the standing position, the percentage increase in norepinephrine levels was significantly lower in the luteal phase and correlated inversely (r= - 0.7031;p > 0.0001) with the baseline estradiol values. Therefore, the sympathetic response to a physiological stress is attenuated, during the luteal phase of the menstrual cycle in normal women.