In amytalized cats either complete section of or bilateral transverse lesions of the brain-stem through the pons or upper medulla results in periodic breathing. If the animal has no recording band about the chest the periodicity consists in a period of respiratory stand-still in the expiratory phase, followed by a period of regular respiratory movements. Active inspiration is readily induced during expiratory arrest by applying light pressure over the skin of the chest. When the animal has a recording band about the chest the periodicity consists in a period of respiratory stand-still in the inspiratory phase followed by a period of regular respiratory movements. Touching the mucosa of the pharynx readily inhibits the inspiratory stand-still. Normal uninterrupted as well as rapid breathing (180 per min.) was observed in an animal under light urethane anesthesia with the brain-stem completely sectioned through the caudal level of the pons. It is suspected that the rapid respiration in this animal was of afferent vagal origin.