Two groups of male rats castrated in adulthood were injected daily with estradiol benzoate for 7 days. During the period of injections the subjects were tested for feminine responses to mounts by nonexperimental males. Potassium chloride was applied to the cortices of the subjects in one of the groups before each test, whereas the other group was similarly treated with saline. Both of the groups displayed lordosis responses to mounts, but showed no feminine soliciting responses. The potassium chloride-treated rats exhibited significantly higher lordosis rates than the control subjects. The results suggest that the cerebral cortex exerts an inhibitory influence on the execution of lordosis responses by male rats.