['Endoscopic thoracic (T2-3 or T3-4) sympathectomy (ETS) is a highly effective treatment for palmar hyperhidrosis. Because the T2-3 or T3-4 sympathetic ganglia are involved in direct sympathetic innervation of the heart, sympathectomy at this level may alter baroreflex control of heart rate. The purpose of our study was to examine the influence of ETS on baroreflex responses to pressor and depressor stimuli under small-dose sevoflurane anesthesia. We studied 40 patients with palmar or axillary hyperhidrosis who were scheduled to receive ETS. In the ETS procedure, the sympathetic trunk was identified by using thoracic endoscopy and was transected. Before and after ETS, the pressor or depressor test was performed by using an IV infusion of phenylephrine or nitroglycerin, respectively, under small-dose general anesthesia. Baroreflex sensitivity was calculated from R-R intervals and systolic blood pressure. ETS did not change heart rate and systemic blood pressure at rest, although ETS significantly altered baroreflex in both pressor and depressor tests in all patients. Baroreflex was completely suppressed in 1 of 19 patients in the pressor test and in 9 of 21 patients in the depressor test. We conclude that baroreflex responses are suppressed in patients who receive ETS.'] Does endoscopic thoracic sympathectomy suppress baroreflex control of heart rate in patients with essential hyperhidrosis?