Ten dogs were used for electrostimulation of the sacral roots to improve urethral sphincter closure. To induce and maintain urethral closure in longstanding stimulation, a variety of stimulation patterns was investigated systematically. With continuous stimulation, the induced sphincteric response faded corresponding with the increase in frequency of stimulation applied, but in phasic stimulation with a stimulation/rest ratio of 1:2, strong sphincteric contractions were reproducible after each rest interval. If the stimulation bursts were shortened to 30-60 msec., interrupted by an off-time of again twice the duration of the stimulation, unfused sphincteric tetani were induced, resulting in a sinusoidal oscillating closure pressure that did not drop in the prestimulus baseline during the off-time. A sufficient sphincteric closure pressure could thus be sustained over 1 hour of uninterrupted stimulation.