The behavioral effects of the removal of both temporal lobes, including the uncus and the greater part of the hippocampus, were studied in macaques. The monkeys exhibited the following symptoms: 1) forms of behavior which seem to be indicative of "psychic blindness"; 2) strong oral tendencies in examining available objects (licking, biting gently, chewing, touching with the lips, "smelling"); 3) a strong tendency to attend and react to every visual stimulus ("hypermetamorphosis"); 4) marked changes in emotional behavior or absence of emotional reactions in the sense that the motor and vocal reactions generally associated with anger and fear are not exhibited; and 5) an increase in sexual activity. These symptoms also appeared if the olfactory tracts were cut previous to removing both temporal lobes. Even the oral tendencies, except for the "smelling," were present.The symptoms typical of monkeys with both temporal lobes removed did not appear after 1) bilateral removal of the first temporal convolution; 2) bilateral removal of the second and third temporal convolutions; 3) severing the connections between the temporal and the frontal lobes, i.e., duplicating the anterosuperior margin of the lesion produced by temporal lobectomy; 4) severing the connections between the temporal and the occipital lobes, i.e., duplicating the posterior margin of the lesion produced by temporal lobectomy. The symptoms also did not appear after unilateral temporal lobectomy, except that there was in some cases a change in the direction of greater "tameness." This "tameness" was also observed when after previous extirpation of both prefrontal areas one temporal lobe was removed.Differential reactions to visual stimuli established preoperatively were seriously disturbed after bilateral temporal lobectomy, but it was possible to reestablish the response through training. The ability to "generalize" in responding to visual stimuli did not seem to be impaired.