The morphology of the normal bladder has been compared with that of the obstructed and the ageing bladder, using both light and electron microscopy. In the normal bladder the smooth muscle cells are closely packed together with relatively little intervening connective tissue. The smooth muscle bundles are innervated predominantly by autonomic presumptive cholinergic nerve fibres, while adrenergic nerves are usually observed in association with blood vessels. In the obstructed bladder, many smooth muscle cells are surrounded by large amounts of connective tissue and some of the muscle cells change their function from contracting to seemingly being involved in collagen synthesis. A significant reduction in the innervation of the smooth muscle cells is observed. In the ageing bladder, the smooth muscle cells have a normal morphology which is in contrast to the findings in the obstructed bladder. A reduction in the innervation of the ageing bladder is observed, although to a considerably lesser extent than that observed in the obstructed bladder. As the morphology of the obstructed bladder differs from that of the ageing bladder, it is unlikely that the changes seen in the obstructed bladder simply reflect a function of age.