The extrinsic efferent nerve fibres to the urinary bladder in the cat were studied by secondary degeneration after transection of the seventh lumbar, all three sacral and the first coccygeal ventral roots of spinal nerves and after extirpation of both hypogastric ganglia. Under the electron microscope, degenerated nerve fibres of spinal origin could be observed in the trigone region among the ganglion cells and all layers and in the different areas of the urinary bladder wall. These degenerated nerve fibres containing mainly clear vesicles, 30–60 nm in diameter, and a few 80- to 120-nm granular vesicles were situated in synapsing contacts on the surface of the local nerve cells and in synapsing with other probably local nerve processes. After extirpation of the hypogastric ganglia several degenerated nerve fibres could be found along the blood vessels and lymph vessels in all layers. However, occasionally on the surface of the local nerve cells degenerated nerve fibres could also be found. 2 months after both interferences most of the nerve fibres and synapses remained unaffected. According to these observations the extrinsic efferent nerve fibres and synapse seem to have a modulatory effect on the local ganglia. The large amount of the local intact synapses suggests that the micturition reflex is not a spinal but a local peripheral reflex.