Ten men with longstanding idiopathic Parkinson's disease (IPD) were investigated by urodynamic and electromyographic methods. The urodynamic studies were repeated after stopping anti-Parkinsonian medication for several hours. All patients showed a difference between the two studies, but the changes were unpredictable. Three patients who had high residual urine volumes in both studies were thought to have prostatic obstruction. EMG analysis showed no evidence of a lower motor neurone lesion affecting the striated urethral sphincter. It was concluded that micturition difficulty in the patient with IPD is due to detrusor hyperreflexia, influenced by the basal ganglia, which is not associated with impaired striated urethral sphincter activity.