After ejaculation, the male rat emits an ultrasonic (22-kHz.) vocalization. This sound is produced repeatedly until about three fourths of the postejaculatory interval has elapsed. In this study, the occurrence of the vocalization was described, and physiological and behavioral evidence was presented that the postejaculatory vocalization reflects an inhibitory state that underlies the postejaculatory refractory period. The vocalization period was characterized by a predominance of slow-wave, spindling, sleep-like electroencephalographic activity. Electrical shock was able to stimulate mating responses only after the cessation of the vocalization period. It was concluded that an absolute refractory period of the postejaculatory interval lasts until the end of the vocalization period and that the time from the termination of the vocalization until the resumption of mating is a relative refractory period
