&NA;High upper thoracic sympathectomy using microsurgical techniques aided by electrical stimulation of the sympathetic chain is described. Use of the microscope facilitates identification and dissection of the sympathetic chain and minimizes the risk of pleural damage. Electrical stimulation of the sympathetic chain establishes the correct functional level for surgical excision. At the correct level, the threshold for piloerection, sudomotor response, and decrease in blood flow of the ipsilateral hand to electrical stimulation was minimal, and a six‐fold increase in stimulus current causing current spread was required to dilate the ipsilateral pupil. After identification of the proper level, surgical excision can be done without risking postoperative Horner's syndrome. Excision of the appropriate ganglia and intervening sympathetic chain with placement of surgical clips on the proximal and distal nerve stumps provides tissue for histological analysis, decreases the opportunity for regeneration, and facilitates localization on postoperative x‐rays. (Neurosurgery24:449‐452, 1989)