ABSTRACTThis study tested the hypothesis that the palmar galvanic skin response (GSR) involves the sweat gland and an epidermal component each responding preferentially according to the demands of the behavioral situation. Their relative contributions were determined by comparison of simultaneous GSR's from areas with high vs low concentrations of sweat glands and with direct measurement of vapor production as well. Stimuli were tones and lights which were either alerting signals or execution signals for a perceptual or a motor (reaction time) task. The population unexpectedly showed greater relative sweat response to the alerting signal for the reaction time task than to the associated execution signal (71 out of 94 S's). Individual subjects, but not the population as a whole, differentiated significantly between alerting and execution signals for the perceptual task. Results supported the hypothesis that two components present in thepalmarGSR manifest stimulus response specificity, but were inconclusive regarding the nature of the class of stimuli to which each responds. The difference can not depend on preparation for motor as opposed to non‐motor activity. GSR, Sweat vapor. Sweat gland, Epidermal, Tones, Lights, Alerting, Response specificity, Adaptive behavior. (R. Edelber