Background and Aims: To measure the extended renal hemodynamic changes induced by intravenous radiocontrast. Methods: Cross-ewes were studied in a randomized cross-over study. Intravenous saline or radiocontrast were administered, and continuous measurement of cardiac output and renal blood flow (RBF) was performed with flow probes. Results: Radiocontrast induced early but transient increases in cardiac output with vasodilatation, followed by return to baseline values within 2 h. There was an initial decline in RBF (a??5.2 A? 4.5 vs. 2.1 A? 5.3 ; p <0.0001) and decreased renal vascular conductance (a??4.0 A? 7.2 vs. 3.3 A? 7.1 , p <0.0001; vasoconstriction). This renal vasoconstriction resolved within 2 h and was followed by sustained (72 h) renal vasodilatation with higher RBF (270 A? 13 vs. 236 A? 11 ml/min; p <0.0001). Conclusions: Radiocontrast induces short renal vasoconstriction followed by sustained vasodilatation and increased RBF. Short-term studies are not representative of the overall sustained renal hemodynamic effects of radiocontrast.