Changes in the visualization of non-ionic contrast medium (Omnipaque 300) in the urography by DIP were monitored for the normal sided urinary tract in patients with urolithiasis using a densitometer. In addition, changes of the visualization in relation to the dose of contrast medium used was examined and compared with that of ionic contrast medium (60% Urografin). The optimum photographing time was 15 minutes in the upper urinary tract (nephrogram, calyx, pelvis, upper ureter) and 20 minutes in the lower urinary tract (lower ureter, urinary bladder). Visualization of high usefulness appeared to be obtainable for the imaging diagnosis by DIP in subjects with normal renal function even when the photographing was completed 20 minutes after infusion of contrast medium. In relation to the doses of contrast medium used, no difference was observed in the variation pattern but a better imaging was obtained in the 100 ml group than 50 ml group with a significant difference (P less than 0.01) in the 15-20 minute images of the calyx and pelvis of the kidney and urinary bladder in particular, this suggested the high usefulness of 100 ml dosing for the imaging diagnosis. In the visualization of ionic contrast medium, some difference was observed in the variation pattern and the visualization was better in Ominpaque 300 groups than in 60% Urografin group with a significant difference (P less than 0.01) in the 15-20 minute images of the calyx and pelvis of the kidney and urinary bladder. This suggested the high usefulness of non-ionic contrast medium.