Continuous, high volume, venous-venous haemofiltration was used as renal support in 28 critically ill patients with acute renal failure. Fifteen patients survived and were subsequently discharged from the ITU. Although haemofiltration was highly effective in reducing the blood urea and serum creatinine, only survivors demonstrated a significant increase in arterial pH (medians before and at two days 7.28 and 7.49 respectively, p<0.005) with="" a="" reduction="" in="" severity="" of="" their="" illness="" (median="" apache="" ii="" scores="" before="" and="" at="" two="" days="" 23="" and="" 16,="">p<0.005). patients="" who="" died="" remained="" severely="" ill="" and="" acidotic="" (median="" apache="" ii="" scores="" before="" and="" at="" two="" days="" 26="" and="" 28;="" median="" arterial="" ph="" values="" 7.32="" and="" 7.31="" respectively)="" and="" by="" day="" two="" of="" treatment,="" marked="" differences="" between="" the="" patient="" groups="" in="" apache="" ii="" scores,="" mean="" arterial="" pressure,="" arterial="" ph="" and="" urine="" flow="" rate="" had="" developed.="" haemofiltration="" with="" the="" correction="" of="" acute="" uraemia="" alone="" does="" not="" necessarily="" lead="" to="" a="" reduction="" in="" the="" severity="" of="" illness="" which="" in="" the="" critically="" ill="" more="" frequently="" reflects="" other="" organ="">