The contractile effects of a commonly used radiographic contrast medium, sodium diatrizoate and meglumine diatrizoate, were examined on isolated canine renal arteries. Rings of renal artery, with and without endothelium, were mounted in organ chambers filled with Krebs-Ringer bicarbonate solution to record isometric tension. Both preparations contracted comparably to increasing concentrations (10(-9) to 10(-4) mol/L) of norepinephrine, and only rings with endothelium relaxed with the application of acetylcholine. The contractile responses of the rings to increasing concentrations of either contrast medium or osmotically matched solutions of glucose were similar, suggesting that the primary factor for contraction was the osmolality of the bathing solution. No significant differences were observed between the responses of rings with and without endothelium, suggesting that the endothelium did not influence the contractile response. After exposure to the hyperosmotic solutions, rings were again tested for relaxation with acetylcholine. Rings that were prepared with endothelium relaxed with the application of acetylcholine, suggesting that functional properties of the endothelium were not affected by the hyperosmotic media. The results of this study indicate that the vasoconstrictor effects of radiographic contrast media such as meglumine/sodium diatrizoate are related to increased osmolality and are not influenced by the presence of endothelium.