Continuous arteriovenous haemofiltration (CAVH) was employed in ten patients with acute renal failure using an AN-69 plate filter. Special measures were taken to improve the efficiency of the technique, including the use of short, large-bore catheters for vascular access, predilution infusion of the substitution fluid, and moderate vacuum suction to the ultrafiltrate compartment. In five patients continuous arteriovenous haemodiafiltration was performed by the addition of slow dialysis at a dialysate flow of 1 litre per hour. This technically simple manoeuvre enhanced solute clearances up to 20 ml/min and obviated the need for standard intermittent dialysis sessions in all cases. Repeated measurements of transmembrane pressure and ultrafiltration rate permitted calculation of the in vivo membrane permeability index, which showed a reproducible decline with time. With relatively low heparin requirements an adequate filter performance could be maintained for over 48 h. The encouraging clinical results indicate that CAVHD, in spite of the invasive nature of this technique, may be considered a first-choice treatment for patients with acute renal failure in the intensive care unit.