Abstract The effects of hippocampal lesions were investigated in cats with and without commissurotomies during tactile discrimination learning. Acquisition of the response was not affected in any of the subjects. Deficits in reversal performance occurred in both paws following bilateral hippocampal lesions, and in the paw contralateral to the lesion if forebrain commissures were sectioned. Deficits in extinction of the response occurred only after bilateral hippocampal lesions. The most severe deficits were found during extinction of the discrimination in split-brain subjects with unilateral hippocampal lesions. These deficits were always in the limb contralateral to the hippocampal lesion. It would appear from these results that hippocampal damage interferes with activities involving alteration of a stabilized habit.