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Audible and ultrasonic cries of five species of myomoph rodent pups were generally found to be closely associated with the onset of the expiratory phase of respiration (recorded with a hot wire anemometer). Consideration of the patterns found and possible laryngeal mechanisms may help to explain the origin of the ultrasounds which differ considerably in physical structure from the typically “vocal” audible cries. Echolocation cries of the constant frequency bat Rhinolophus luctus were always associated with expiration, whereas the much shorter cries of two vespertilionids, Eptesicus serotinus and Plecotus auritus, although occurring at the onset of expiration at low repetition rates, could occur throughout the respiratory cycle at the highest rates recorded. The patterns found may well be adapted for the echolocation requirements of these bats. Using a simpler technique the long ultrasounds of adult rats were also found to be associated with expiration.