The mechanism(s) involved in determining the voiding cycle of the rat urinary bladder have been investigated in urethan-anesthetized animals. Fluid emission is almost confined to that phase of the voiding cycle which is characterized by the presence of a series of high-frequency oscillations in intraluminal pressure (IPHFO). During this phase the mean urethral flow rate reached a maximum and fluid was expelled in a stream-like fashion. The index obtained by multiplying the amplitude of IPHFO by their duration was significantly related to the maximal value of urethral flow rate. The IPHFO were selectively abolished by administration of d-tubocurarine at a dose that barely affects detrusor contractility. Moreover, d-tubocurarine reduced mean urethral flow rate and increased residual volume. The reflex (hexamethonium sensitive) mechanism(s) responsible for the generation of IPHFO is more developed in male than female rats. This mechanism, which involves activation of skeletal muscle, plays a significant role in determining bladder voiding in this species.