The visualization of non-ionic contrast medium (Omnipaque 300) in the excretory urography by bolus injection was examined with regard to the normal sided urinary tract in patients with urolithiasis using a densitometer and further compared with that of ionic contrast medium (60% Urografin). In relation to the photographing method, both contrast media showed an increasing frequency of high opaque site in the order of Tomo, A-P and P-A images, which tended to shift from the upper to the lower urinary tract. In relation to the site of determination, both agents showed a good image in the upper urinary tract by the each photographings, while P-A image was better than A-P image in the lower urinary tract, suggesting their high usefulness for the imaging diagnosis. The visualization in relation to the contrast medium used was better in Omnipaque 300 groups than in 60% Urografin group with a significant difference (P less than 0.05-0.01) in the calyx and pelvis of the kidney by the each photographings, suggesting a high usefulness of non-ionic contrast medium. A densitometer seemed to be a useful means for evaluation and examination of the visualization with excellent objectivity as compared with conventional macroscopic methods.