The coordination between the renal pelvis and ureteral peristalsis is an important part of the hydrodynamics of the upper urinary tract. Pelvic pressure and frequency of ureteral peristalsis were registered simultaneously in 28 adult, female dogs. A mathematical analysis of these observation showed a non-linear relation of a "power function" in approximately 85% of the investigations. Hysteresis was demonstrated between the power functions of the increasing and of the subsequent decreasing diuresis in 15 of the examined dogs. It was concluded that the renal pelvis in a monocalyceal system governs the frequency of ureteral peristalsis and that hysteresis represents a viscoelastic action of the smooth muscle tissue.