This is a detailed report on neuropsychiatric findings in six years of study of fifty cats and forty monkeys. During control periods the animals were studied and rated for individual and social characteristics and their ability to learn various skills. Neuroses were induced in twenty-three cats and eighteen monkeys by exposure to adaptational conflicts. The animals were then subjected to cerebral operations. Data are incomplete, but suggest that the effects vary not only with the site and extent of the lesions but also with the preoperative experiences of each animal and its postoperative care and retraining.