The normal pattern of breathing movements in Rana pipiens has been studied by recording pressure and volume changes in the buccal cavity and lungs, and electromyograms from the muscles involved in this activity. Two types of breathing movement were obtained, one concerned with ventilation of the buccal cavity (buccal cycles) and the other with lung ventilation (lung cycles). Only in the latter type of movement were the nares and glottis actively involved. During buccal cycles the nares remained open and the glottis closed, so although excursions of the buccal floor were some two-thirds of the magnitude of those occurring during lung cycles, only low pressures were generated. The onset of a lung cycle was signalled by activity in the laryngeal dilator muscle. When the glottis opened, lung pressure and volume decreased, and buccal cavity pressure and volume increased. After closure of the nares, the buccal floor was rapidly elevated by the activity of the breathing muscles and air was forced into the lungs from the buccal cavity. At peak pressure in the lungs and buccal cavity the glottis closed and nares opened. The recovery stroke of the buccal pump was passive. No evidence was found for large pressure differentials between the buccal cavity and lungs when the glottis was open, and air-flow recordings at the external nares showed two phases of flow during each buccal cycle and four phases with each lung ventilation cycle.