Stimulation of reticular formation or associated pathways in 6 Macaca mulatta, ranging in sites from the anterior nucleus of hypothalamus to the median raphe of pons, using electrodes of enameled number 50 stainless steel wire, coated with Taggon no. K13 paint, produced changes in animals'' ability to perform a learned procedure. The parameters of the square-topped monophasic stimuli approximated (1) frequency 350 cps, (2) duration 0.2 milli second, (3) voltage 0.2 - 1.2 volts, (4) delay 0.1 milli sees. The most reliable impairment occurred during continuous stimulus (5 sec). Eeg''s were recorded from depth and scalp electrodes prior to stimulation.