The study was designed to examine the time-course of iodine elimination by hemodialysis to determine a desirable duration for dialysis after angiography to prevent contrast media nephropathy (CMN) in patients with renal failure. Reduction rates of iodine by hemodialysis (DRR) of 1 to 3 h and the renal elimination of iodine (RER) for 20 h after hemodialysis were prospectively examined in 8 chronic renal failure (CRF) patients. The mean DRR was 46.6% at 1 h, 65.2% at 2 h, and 75.1% at 3 h, and the mean RER was 49.4% in the CRF patients. Renal function significantly deteriorated in 2 CRF patients after angiography. Plasma iodine was eliminated by more than 80% after 2 h of hemodialysis following angiography, and the subsequent renal elimination in patients with mild-to-moderate renal failure was also examined. There is no need of prophylactic hemodialysis to prevent CMN for these patients when they have no additional risk factors such as a high dose of contrast medium, diabetes mellitus, or severe heart failure. However, 2 h of hemodialysis is desirable immediately after angiography for patients with moderate renal failure and one additional risk factor, and three hours or more of hemodialysis is also desirable for patients with severe renal failure, and for those with moderate renal failure having two or more additional risk factors.