Two groups of patients who developed denervation of the bladder after excision of the rectum for carcinoma have been studied by histological examination of bladder biopsies. The groups were compared with a group of control patients of a similar age. One group with denervation of the bladder was studied soon after (7 weeks) and the other group in the long term (10 months) after operation. Bladder biopsies were stained for acetylcholinesterase, catecholamines and connective tissue. Tissue was also processed for electron microscopy. In control patients, the ratio of cholinesterase positive nerves to the number of smooth muscle nuclei (24:100) was significantly greater than in patients with denervation of the bladder studied soon after operation (2.5: 100; P less than 0.01). Appearances consistent with degenerate nerve terminals were observed on electron microscopy in these patients. No increase in the density of adrenergic nerves was observed in either group of patients with denervation of the bladder. In the long term, a greater density of cholinergic innervation was noted compared with patients studied soon after operation (P less than 0.05). In addition, nerve terminals, similar in appearance to those of control patients, were observed on electron microscopy. The findings in patients with denervation of the bladder studied in the long term after operation are consistent with partial regeneration of autonomic nerves. They suggest that, whilst histological examination of bladder biopsies may be useful soon after excision of the rectum, they may be less sensitive in the long term.