Following menopause, some women are troubled by hot flashes (episodes of flushing and perspiration), whereas others do not experience the symptom. To determine whether the extent of estrogen deficiency influences the occurrence of the disturbance, the authors measured the levels of estradiol (E2), estrone (E1), and sex-hormone binding globulin (SHBG), and the percent and total non-SHBG-bound E2 in 24 women with frequent hot flashes and 24 women who had never experienced the symptom. Significantly lower levels of E2 (P less than .002), E1 (P less than .05), percent non-SHBG E2 (P less than .05), and total non-SHBG-bound E2 (P less than .01) were found in the symptomatic women. Similar differences were confirmed in 18 subject pairs matched for age, years since menopause, and presence or absence of ovaries. The finding of a significantly (P less than .05) lower percent ideal body weight in the women with hot flashes suggests that the known effects of body weight on the rate of extraglandular estrogen production and the level of SHBG in postmenopausal women may be important variables determining the occurrence of hot flashes.