SummaryWith 13 tame cats as the subjects, of which 10 had bilateral prefrontal lesions, and 3 as the control group with temporal lesion only, a study was carried out on changes occurring in spontaneous behaviors and hypothalamic rage threshold (HRT) after receiving lesions. As a result it has been demonstrated that behavioral changes appear as hyperreactivity, emotional hyperreactivity and perseverative tendencies. As for the changes in the HRT there can be observed instability of HRT, an increase in reactivity, and a rise in HRT of the group without behavioral change. On the basis of these results it has been pointed out that the lateral surface of prefrontal cortext is involved in the process of the organism in incorporating changes of external circumstance into the HRT, and the orbital surface acts inhibitorily on the HRT.