Maximal electrical stimulation (MES) administered from a laboratory device designed to deliver stimulation pulses of relatively high voltages and currents was performed in 29 patients. All had suffered from bladder overactivity for several years, either idiopathic detrusor instability or an uninhibited overactive bladder, and all had failed to respond to conservative treatment. MES was performed in female patients by means of intravaginal and intra-anal electrode carriers and in males by anal electrodes only. In some cases additional stimulation was administered by means of a single needle bipolar electrode inserted directly into the pudendal nerve. Maximal amplitude was attained after gradual increases in amplitude and the patient's adaptation to this. Stimulation was administered by the therapist but the amplitudes were determined by the patient and limited by his/her pain threshold. Alternating rectangular constant voltage pulses at a repetition rate of 10 Hz were used. Treatment consisted of 4 sessions of stimulation with intervals of 1 week between each application. All patients showed a significant increase in functional bladder capacity and 11 reported a 30% decrease in the frequency of micturition. Two patients were unaffected by stimulation with external electrodes but responded well to direct pudendal nerve stimulation. MES seems to be an effective first-line treatment for the uninhibited overactive bladder.