Extracellular recordings were made from ninety-four single motoneurones in the dorsal motor vagal nucleus of chloralose-anaesthetized or decerebrate cats. Fifty-five neurones had axons in cardiac vagal branches and thirty-nine had axons in pulmonary vagal branches; the conduction velocities of the axons were in the C fibre range, i.e. the axons were non-myelinated. The neurons exhibited little or no spontaneous activity. Excitatory and inhibitory synaptic inputs were demonstrated by electrical stimulation of the vagus nerve or its branches. Twenty-four neurones were tested by carotid sinus distension but only one was excited. Iontophoretic excitation of neurones projecting to cardiac vagal branches had no effect on heart rate. The properties of these neurones and their possible functions are discussed and contrasted with those of cardiac and pulmonary vagal motoneurones in the nucleus ambiguus.

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