We examined the kinetics of contrast agent elimination during hemodialysis in 7 patients with end-stage renal disease on regular hemodialysis treatment (group I) and in 13 patients with impaired renal function (serum creatinine 214-657 mumol/l; group II). The nonionic agent iohexol was administered at a dose of 0.4-4.5 g/kg, and a 6-hour hemodialysis was performed with 1-18 h delay. This procedure removed 60-90% (mean 77%) of the iohexol present in the circulation at the start of dialysis treatment. The mean extraction ratio across the dialysis membrane was 0.47 and was inversely related to blood flow. The total clearance of iohexol was 70.4 +/- 24.6 ml/min and was very close to dialyzer clearance, as estimated from blood flow and extraction ratio. The plasma iohexol level after dialysis was related to the dose administered, iohexol clearance, and the patients' body weight. During peritoneal dialysis (36-60 liters dialysis fluid), 43-72% of the iohexol dose was removed from the patients' circulation. In patients of group II no further impairment of the renal function (increase of serum creatinine) in conjunction with angiography was observed. We conclude that hemodialysis and peritoneal dialysis are effective methods for removal of iohexol. Our observations suggest also that accelerated elimination of contrast media by prophylactic dialysis can be beneficial in preventing further reduction in renal function after angiographic procedures in high-risk patients.