In intact cats and cats with the mesencephalon transected the intravenous administration of sodium butyrate and related compounds (0.3 to 3 millimoles per kilogram) induced the so-called paradoxical phase of the sleep, as indicated by electroencephalograms, electromyograms, heart rate, respiration, and eye movement. This phase appeared after a 3- to 5-minute period of sleep characterized by slow waves, and continued for 4 to 15 minutes.