1. The characteristics of the mass reflex responses recorded from the postganglionic branch (N. caroticus internus) of the superior cervical ganglion following afferent nerve stimulation were studied in cats anaesthetized with chloralose. 2. The postganglionic reflex produced by a single volley in low threshold cutaneous or high threshold muscle afferents consisted of two initial and two more irregular, later and smaller components. All reflex components showed considerable variations both in latency and amplitude. 3. The reflex discharges were followed by a post-excitatory depression both of the spontaneous discharges of the postganglionic fibres (silent period) and of the effects of a consecutive afferent volley. The depression was complete from about 45 to about 150 ms after the afferent volley entered the spinal cord. Full recovery took more than 1,200 ms. 4. Brief tetanic stimuli (1 to 10 pulses, 100 to 300 Hz, max. train duration 45 ms) enhanced all reflex components. The excitatory effects of afferent volleys entering the spinal cord more than 45 ms after the first one were suppressed by the post-excitatory depression initiated by their predecessors. 5. A comparison of these results with those obtained when recording from the preganglionic trunk and with those obtained in previous work studying impulse transmission in the superior cervical ganglion revealed that this ganglion transmits the preganglionic reflex discharges in a remarkably faithful manner. 6. It is concluded that the characteristics of somatically induced post-ganglionic reflex discharges depend largeley on the properties of the spinal and supraspinal sympathetic reflex centers, the sympathetic ganglia acting solely as relay in the efferent pathway.