In a group of patients in whom bladder outflow obstruction had been confirmed urodynamically, quantitative assessment of the amount of autonomic nerve in detrusor biopsy samples has been carried out using light and electron microscope techniques. In each specimen allowance was made for muscle cell hypertrophy and increases in connective tissue, both of which occurred in response to bladder outflow obstruction. Similar quantitative assessment was performed on bladder biopsy samples from a group of unobstructed 'control' patients. When the results from the two groups were compared a statistically significant reduction in the amount of autonomic nerve supplying detrusor muscle was demonstrated in the obstructed group. This finding provides additional evidence that functional impairment of the urinary bladder occurs in response to outflow obstruction and emphasizes the need for prompt relief of the condition.