Spontaneous alternation behavior was investigated in rats with electrolytic lesions in the septal region and in sham-operated controls. Bilateral septal lesions abolished alternation, as both the overall alternation rate and the distribution of daily scores were very close to 50-50 chance expectancies. In contrast, the sham group alternated at a very high rate. The present results are consistent with the hypothesis that spontaneous alternation is the result of an underlying inhibitory process.