Electrolytic lesions restricted to either the medial or the dorsolateral septal area were made in rats previously implanted with chronic recording electrodes in the hippocampal formation. The former, but not the latter, lesion disrupted hippocampal theta activity. Rats with both kinds of lesion, as well as operated controls, were trained to barpress for food pellets on a schedule of differential reinforcement of low rates with an interresponse requirement of 20 sec. Both lesions impaired task efficiency to an equal degree, but neither prevented the development of a timing curve. This pattern of results is consistent with the behavioral inhibition hypothesis of septal function, but the failure to dissociate the effects of the two lesions is discordant with observations in other tasks apparently requiring response inhibition.