Following the injection of 3-5 microliters of horseradish peroxidase or Fast Blue into the left adrenal medulla, labelling of neurons in the vagal sensory ganglia of rats and guinea-pigs has been demonstrated in all cases. Labelled vagal motor neurons with cell bodies in the dorsal motor nucleus of the vagi have been demonstrated in all cases in the guinea-pig and occasionally in the rat. The possible reasons for this variation are discussed. In both rat and guinea-pig the motor and sensory vagal innervation of the rat adrenal is derived from bilaterally situated cell bodies and the proportion of innervation derived from the two sides is approximately equal but with a slight ipsilateral predominance.