1. Injury to the inferior colliculi causes considerable weakening or even total disappearance of the motor component of the orienting reflex. Other investigated components (electroencephalographic, cardiac, respiratory, psychogalvanic) remain unchanged. Manifestation of the components of the orienting reflex to photic stimuli is identical in normal and experimental cats. 2. Lesions of the inferior colliculi modify the course of extinction of the orienting reflex to acoustic stimuli: extinction of the somatic (electromyographic), component takes place faster than in normal animals, but autonomic and encephalographic components are extinguished more slowly. 3. Differences observed in manifestation and extinction of the orienting reflex folliwing injury to the inferior colliculi indicate the complex morphological and physiological organization of this reflex and differences in the participation of individual brain structures in its manifestation and extinction. 4. Disturbances of conditioning and of spatial analysis of acoustic stimuli in animals with lesions of the inferior colliculi are linked with depression of the somatic component of their orienting reflex, essential for the localization of acoustic stimuli.