Sensory response properties of putamen neurons were investigated in 4 awake macaque monkeys while the animals performed GO/NO-GO tasks guided by sensory stimuli. In the GO condition, visual stimuli served as a trigger for a sequence of repetitive elbow flexion-extensions and auditory stimuli served as a trigger for orofacial movements, while the identical sensory stimuli required the animals to withhold movements in the NO-GO condition. Short latency responses to visual and/or auditory stimuli were observed in 206 type I cells with tonic discharges at about 2-7 Hz, with a characteristic discharge rhythm and in 57 type II cells with low spontaneous discharge rates, usually less than 0.5 Hz, which showed burst discharges during the tasks. Most of these cells (163/206 type I cells, 52/57 type II cells) responded differentially to identical sensory stimuli presented in the GO and NO-GO conditions. The responses to sensory stimuli presented in the GO condition were much larger in 67% of type I cells and 58% of type II cells than the responses to identical stimuli presented in the NO-GO condition. On the other hand, 12% of type I and 33% of type II cells showed larger responses in the NO-GO than in the GO condition. It is suggested that the strong behavioral modulation of striatal sensory responses serves as a mechanism to start the neural processes for preparation and/or initiation or withholding of particular movements associated with learned sensory stimuli.