The cellular mechanisms that underlie the initiation and propagation of the peristaltic contractions, which transport urine from the kidney to the bladder for storage, remain little understood. Extracellular and intracellular microelectrode recordings have identified two populations of smooth muscle cells as well as a population of renal interstitial cells (RICs) that all display spontaneous electrical activity. By analogy with the heart it has been proposed that atypical smooth muscle cells, preferentially located in the very proximal regions of the renal pelvis, generate the essential pacemaker signal. These pacemaker potentials propagate to neighbouring typical smooth muscle cells or RICs to trigger action potential discharge. These action potentials then propagate distally to trigger other bundles of typical smooth muscle cells. The frequency of action potential discharge and contraction decreases as the relative number of RICs and atypical smooth muscle cells compared to typical smooth muscle cells decreases with distance from the renal fornix. It is clear that functional capsaicin-sensitive sensory afferents and the endogenous release of both tachykinins and prostaglandins are essential in the maintenance of normal peristalsis, as well as in monitoring and responding to any chemical or mechanical stimulation. However, the cellular mechanisms underlying the action of these endogenously-released agents remain to be elucidated. Experimental Physiology (2002) 87.2, 129-146.