1. The distribution and properties of 146 brain stem units whose activity was influenced by electrical stimulation of sinus, glossopharyngeal, aortic and superior laryngeal nerves were studied in cats. 2. Cells excited by electrical stimulation of one or more of the nerves were distributed throughout the brain stem in an area extending rostrocaudally from Horsley—Clarke co‐ordinates P 7·5 to P 16·5 and laterally between 1·5 and 5 mm from the mid line. 3. Most of the units excited (n = 129) or inhibited (n = 17) by nerve stimulation were localized in the nucleus reticularis gigantocellularis and nucleus reticularis parvocellularis. 4. The latencies of activation varied from as short as 1·5 msec to as long as 35–40 msec. A high degree of convergence was observed. 5. Evoked responses varied from single spikes to bursts of impulses, the frequencies of which were sometimes as high as 1000/sec following a single shock to the nerve. 6. Spontaneously active cells inhibited (seventeen) by nerve stimulation were located primarily in NRG and NRP. None of the cells was inhibited by stimulation of one nerve and excited by stimulation of the others. 7. The responses of cells to a sudden rise in carotid sinus pressure were similar in kind to the responses to electrical stimulation of the nerves.