Iopamidol, a new, nonionic contrast agent, was evaluated in 18 patients undergoing excretory urography. None of the 18 patients experienced any side effects or adverse reactions. No abnormalities were noted in serum chemistries, complete blood cell counts, urinalyses, or electrocardiograms. The half-life of iopamidol in 17 patients with normal renal function was 2.5 hr. The urograms were judged to be of good or excellent quality in 15 of 16 patients using doses of 200 and 250 mg l/kg of iopamidol. Two patients who were studied using a dose of only 120 mg l/kg had urograms rated poor. Fifteen iopamidol urograms (mean iodine dose, 17.4 g) were compared in a blind fashion with 15 meglumine diatrizoate studies (iodine dose, 29 g). No qualitative difference could be detected between the two groups of urograms. Iopamidol may provide equal-quality diagnostic studies with a lower iodine dose and perhaps greater safety than the currently used ionic agents.