['To determine the effects of clonidine, which reduces central sympathetic activation, on the sweating threshold in postmenopausal women with and without hot flashes.', 'Laboratory physiologic study.', 'University medical center.', '12 healthy postmenopausal women reporting frequent hot flashes and 7 reporting none.', 'In two separate sessions, participants received a blind intravenous injection of clonidine HCl (2 microg/kg of body weight) or placebo, followed by body heating.', 'Core body temperature, mean skin temperature, sweat rate, sternal skin conductance level, and blood pressure.', 'Symptomatic women had significantly lower core body temperature sweating thresholds than asymptomatic women after receiving placebo. Clonidine significantly increased this threshold in symptomatic women but lowered it in asymptomatic women.'] Does clonidine raise the sweating threshold in symptomatic but not in asymptomatic postmenopausal women?