Urinary bladders from mature cats, fixed in various degrees of distension, were studied with silver staining techniques under the light microscope, and with the electron microscope. Ganglia were located primarily in the adventitia, although small collections of perikarvons were located in nerves within the muscle coat. Large nerve trunks enclosed in perineural epithelium penetrated from the adventitia into the muscle coat, giving rise to smaller nerves which ran in the space between muscle fascicles. Small nerves entered each muscle fascicle, giving rise to final branches characterized by extreme tortuosity. There was less kinking and coiling of nerve fibers in bladders fixed in a more distended state. Encapsulated endings and myelinated fibers were scarce. Within a muscle fascicle, nerves were scant. Terminal branches intertwined among the individual smooth muscle cells as free nerve endings. Terminal axons continued to be ensheathed by Schwann cells. Neuromuscular synapses were characterizd by retraction of the Schwann cell from one side of the axon, presence of synaptic vesicles, and synaptic gaps of 400–600 Å. Areas of close contact between flattened and interdigitating parts of adjacent smooth muscle cells were common. Membrane complexes of pinocytotic vesicles and endoplasmic reticulum were distributed around the periphery of individual smooth muscle cells. Smooth muscles cells appeared to vary in the density of their myofilament content.