In critically ill patients with acute renal failure and unstable circulation, dialysis employing conventional haemodialysis may prove technically difficult. If, however, continuous arterio-venous haemofiltration is employed, the haemodynamic problems may be overwon but the method does not always provide effective control of azotaemia. Continuous arterio-venous haemodialysis (KAVHD) is a combination of ultrafiltration and dialysis. The efficacy of KAVHD was investigated retrospectively in 23 critically ill patients with acute renal failure and unstable circulation. All of the patients achieved acceptable steady state concentrations for serum creatinine and carbamide. Four out of five patients with hyperkalaemia obtained normal serum potassium after the first 24 hours of treatment with KAVHD. The average filtration volume was 6.1 1/24 hours, sufficient to provide parenteral nutrition and intravenous infusion and to maintain the negative fluid balance simultaneously. Fifteen patients (65%) died during the intensive course of treatment but none died from complications of KAVHD or renal failure. Renal function was reestablished in eight patients and seven of these could be discharged alive. KAVHD is an effective and simple method of treating critically ill patients with acute renal failure and unstable circulation.