An earlier study of operant conditioning of the GSR was replicated. 2 groups of 15 Ss were run in a totally dark room. After a 10-min, rest, the Contingent (C) group received a dim light following unelicited GSRs for 16 min., then 10 min. of extinction. The Noncontingent (N) group received the same number of lights per min. during reinforcement, when no GSRs were occurring. The dependent variable was the percentage of responses per min., using the average of the last 5 min. of rest as a baseline. Group C emitted significantly more responses during reinforcement and extinction than Group N (p < .01). The groups converged during extinction (p < .05). It was concluded that the unelicited GSR can be conditioned instrumentally. (PsycINFO Database Record (c) 2006 APA, all rights reserved)