The effects of dorsofrontal cortical ablations and of graded, bilateral, subtotal lesions in the caudate nuclei upon the acquisition, extinction, retraining, and further extinction of an avoidance response in cats were investigated. Caudatectomies were performed in two stages, the first stage consisting of dorsofrontal decortication. Prior to initial avoidance training, 15 cats were unoperated, 24 cats sustained dorsofrontal decortication, and 6 were caudatectomized. Following acquisition of the avoidance response, 7 unoperated cats underwent dorsofrontal decortication, and 17 dorsofrontal decorticates were caudatcctomized. Damage to the heads of the caudate nuclei ranged from about 5% to 90%. Preacquisition caudatectomies involved up to about 30% of the nuclei and showed no marked effects relative to dorsofrontal decortication. No data were available on the possible effect of larger caudate lesions on initial acquisition. Dorsofrontal decortication resulted only in slightly lowered resistance to extinction after both acquisition and retraining. With respect to avoidance behavior acquired after dorsofrontal decortication but prior to caudatectomy, resistance to extinction, number of trials required for retraining, latency of escape-responding in retraining, and postretraining resistance to extinction appeared to be functions of caudate lesion magnitude. Small lesions resulted only in low resistance to extinction prior to retraining. Larger lesions further reduced resistance to extinction and also retarded retraining. With damage to over 50% of the heads of the caudate nuclei, escape-response latency was increased. Postretraining resistance to extinction decreased with increasing lesion size. Massive caudate lesions were associated with failure to achieve the retraining criterion in 1,020 trials, and, in one case, complete failure to avoid. Resistance to extinction was the only measure sensitive to dorsofrontal decortication and small caudate lesions. It was suggested that the effects of caudate lesions be viewed as in some way disturbing stimulus functions of feedback from the postures and movements of the organism. (PsycINFO Database Record (c) 2006 APA, all rights reserved)