SUMMARYA double blind randomised trial of two urographic contrast media was performed on two hundred patients with normal renal function and no significant urological abnormality. One hundred patients were given Conray 420 (sodium iothalamate), and one hundred received Urografin 370 (mainly methylglucamine diatrizoate with a small amount of sodium diatrizoate). The same amount of iodine, 300 mg per kg B.W., was given to each patient. The only significant urographic difference was an inferior demonstration of the pelvicalyceal system with Urografin 370. No serious reactions were encountered but of the minor side effects, pain at the injection site, pain in the proximal part of the arm, and a metallic taste were significantly more frequent with Conray 420. There was no relationship between individual side effects and the presence or absence of anxiety. No significant change in blood pressure or pulse occurred with either contrast medium.