Radiographic contrast media (CM) (meglumine/sodium diatrizoate-76%; 1650 mOsm/kg) and other hypertonic solutions induce renal vasoconstriction by an unknown mechanism. In anesthetized dogs, renal blood flow (RBF) was measured with an electromagnetic flowmeter and filtration fraction (FF) and glomerular filtration rate (GFR) by the renal extraction of technetium-99m tin chelate. Ureteral pressure (UP) and wedged renal venous pressure (VP) were measured as indices of intrarenal pressure. Measurements of renal length (L), along with pressures, made it possible to examine the compliance of the system. A 4-cc intrarenal bolus of CM caused a 59% reduction in GFR (control: 0.63 +/- 0.04 to 0.26 +/- 0.04 ml/min X g, mean +/- SEM), in association with a 23% reduction in RBF (control: 3.10 +/- 0.11 to 2.39 +/- 0.26 ml/min X g) and a 44% decrease in FF (control: 0.32 +/- 0.01 to 0.18 +/- 0.03). These responses were compared with a 3-microgram intrarenal bolus of norepinephrine (NOREPI) which resulted in a 79.0 +/- 7.5% reduction in RBF, 68.3 +/- 7.3% reduction in GFR and 42.6 +/- 15.6% increase in FF. The NOREPI-induced vasoconstriction caused transient decreases in renal L, UP, and VP, whereas the CM-induced decrease in renal blood flow was associated with increases in these parameters. In studies employing ureteral occlusion to elevate intrarenal pressure, the magnitude (area, cm2) of the CM-induced decrease in renal perfusion was accentuated with increased UP (r = 0.79, n = 24, P less than 0.001). The CM-induced increase in renal L, UP, and VP must reflect osmotic forces and an increase in intrarenal pressure. The decreases in FF and GFR probably reflect Starling forces in the glomerular capillaries, with osmotic transients dominating. The results suggest a mechanical mechanism for the CM-induced decrease in RBF.