Adrenergic innervation of the human urinary bladder was studied in vitro in specimens excised during operation from 6 neurologically normal bladders and from 5 parasympathetically denervated (lower motor neuron lesion) bladders. Using a specific histochemical fluorescence technique, the adrenergic nerve terminals of the detrusor of the patients with lower motor neuron lesions were thicker, had a stronger fluorescence intensity and were in most cases also more densely distributed than those of any of the 6 neurologically normal bladders examined. By recording the changes in the isometric tension of detrusor strips after different pharmacologic treatments, the existence of .alpha.-adrenergic receptors was demonstrated in the parasympathetically denervated detrusor but not in the normal detrusor. The influence of .alpha.-adrenolytic treatment (phenoxybenzamine) was studied in vivo in 7 patients with lower motor neuron lesions. In the cystometrograms, the bladders were more hypotonic and the autonomous waves appeared at a higher level of filling or were totally extinguished after this pharmacologic treatment. With an isotonic volume registration method, a bladder volume increase was recorded after .alpha.-adrenergic blockade. Using sphincterometry or urethral pressure profile studies, a decrease in the urethral resistance was observed after .alpha.-adrenolytic treatment.