In this pilot study of the renal circulation we applied the reservoir wave approach, a time-domain method for the analysis of arterial pressure and flow that defines the magnitudes of the series resistances that account for the total vascular resistance of an organ. Renal and systemic pressures and flows were measured in anesthetized dogs. Unilateral infusions of angiotensin II (ANG II) or endothelin-1 (ET-1) decreased renal conductance by 30% and 50%, respectively. These decreases in conductance were accounted for by increases in large-artery resistances by 83% and 79%, respectively, and by increases in microcirculatory resistances by 171% and 275%, respectively. Reservoir resistance did not change with ANG II, but increased by 36% with ET-1. P∞ (the theoretical non-zero pressure at which flow ceases) increased from 28.2 ± 4.5 to 37.0 ± 5.7 mmHg (P<0.01) with ANG II and increased from 32.7 ± 5.9 to 43.7 ± 3.3 mmHg (P<0.05) with ET-1. The marked increase in P∞, particularly with ET-1, suggests a preferential decrease in diastolic renal blood flow. The reservoir-wave approach may provide a useful tool for studying the unique aspects of the renal circulation in health and disease.