To examine the possible relationship between the occurrence of menopausal hot flushes and waking episodes, a study was conducted of nine postmenopausal women with severe hot flushes and five asymptomatic premenopausal women. Measurement of simultaneous changes of finger temperature and skin resistance over the sternum was used as an objective marker of hot flushes. During cumulative sleep 47 objectively measured hot flushes occurred, and 45 were associated with a waking episode measured by polygraphic techniques. In eight of nine subjects, a significant correlation was observed between the occurrence of hot flushes and waking episodes. A similar association was not observed in premenopausal subjects. Estrogen administered to symptomatic patients resulted in significant reductions of both hot flushes and waking episodes. These data suggest the menopausal flushes are associated with a chronic sleep disturbance, and both can be improved by estrogen therapy.