We studied the effect of levcromakalim on the function of the urinary tract in rats. Using anesthetized rats, ureteral peristaltic movement of only the ureter region or the ureter with the kidney was induced by fluid infusion into the ureter lumen. Levcromakalim (0.03 and 0.3 mg/kg, i.v.) exerted a stronger inhibitory effect on the peristaltic movement of the ureter region distant from the pelvis than on that near the pelvis, and the inhibitory effect of levcromakalim (0.03 mg/kg, i.v.) was not antagonized by glibenclamide (0.1 mg/kg, i.v. or 10 mg/kg, i.p.). Topical application of levcromakalim (injection volume, 0.1 ml; 10(-4) or 10(-3) M), which was injected via a vessel near the ureter inhibited ureteral peristaltic movement and the inhibitory effect levcromakalim (10(-4) M), was not antagonized by glibenclamide (10(-3) M) injected via the same route. Levcromakalim (0.3 mg/kg, i.v.) did not interrupt micturition in anesthetized and conscious rats. In conscious rats, the micturition interval was prolonged; and in anesthetized rats, the peak pressure during micturition was reduced. After injection of levcromakalim (0.3 mg/kg, i.v.), vesicoureteral reflux did not occur. In the movements of the ureter, urinary bladder and urethra, levcromakalim exerted the strongest inhibitory effect on the ureteral peristalsis.