In order to mimic and then modify the input to the respiratory centre from pulmonary stretch receptors, the central ends of the cut cervical vagus nerves were electrically stimulated with a frequency determined by transpulmonary pressure through a voltage to frequency converter. At appropriate end-expiratory stimulation frequency and gain of the voltage to frequency converter, such stimulation restored the pre-vagotomised patterns of breathing in rabbits, cats and dogs. Mimicking the changes in activity from pulmonary stretch receptors that would be produced by such manoeuvres as hypercapnia, inflations and deflations, reproduced the responses in inspiratory duration that occurred with natural stimuli in the same animals with intact. There were some differences between the responses of expiratory durations to the natural and mimicked interventions; these may be related to the presence of increased expiratory muscle activity in the former. The results demonstrate that transpulmonary pressure-controlled stimulation of the afferent vagus nerves is a satisfactory method of mimicking and controlling the pulmonary stretch receptor feedback mechanism in studies on the control of breathing.