Unilateral lesions of the caudate nucleus selectively blocked lever pressing with the forepaw contralateral to the lesion; response with the ipsilateral forepaw was not altered. These findings were verified with 2nd-stage lesions of the opposite caudate, although 1-stage bilateral lesions produced more variable effects. Control ablation of sensorimotor cortex typically did not interfere with contralateral response and the integrity of sensorimotor cortex was not necessary for blocking of response induced by caudate lesions. With other operant conditions and FI reinforcing contingencies, bilateral caudate lesions disrupted preoperatively formed response-suppression during early segments of each FI. These data implicate the caudate in sensorimotor functions and some form of inhibitory regulation of behavior.