OBJECTIVE To evaluate the short-term metabolic and haemodynamic effects of continuous veno-venous haemofiltration (CVVH) in critically ill patients with acute renal failure (ARF). METHODS Prospective study of nine consecutive critically ill patients with established acute oliguric renal failure. METHODS A general ICU in an 800-bed university hospital. METHODS Critically ill patients, mean age 56 +/- 6 years. Four had multi-organ failure, one had acute haemolytic uraemic syndrome, one had idiopathic lactic acidosis, two had haemorrhagic pancreatitis and one had urinary sepsis. METHODS All patients were mechanically ventilated with arterial and pulmonary artery catheters in situ. RESULTS Oxygen consumption (VO2), CO2 production (VCO2) resting energy expenditure (REE), continuous blood pressure, heart rate, central venous pressure (CVP), pulmonary artery pressure (PAP), and cardiac output (CO), as well as tidal and minute volumes, end-tidal CO2 and arterial blood gases, were continuously measured for one hour prior to and one hour following the institution of CVVH. Body temperature, arterial blood pressure, heart rate, CVP and pulmonary artery catheter data remained stable throughout the study period. Prior to CVVH, VO2 was 326 +/- 33 ml/min, VCO2 was 245 +/- 27 ml/min and REE was 2241 +/- 231 kcal/24 hours. Following institution of CVVH, VO2 was 324 +/- 33 ml/min, VCO2 was 244 +/- 27 ml/min and REE was 2227 +/- 230 kcal/24 hours. CONCLUSIONS CVVH does not affect metabolic rate and haemodynamic stability in critically ill patients. The lack of any effect on the metabolic rate and haemodynamic parameters in such patients may have significant clinical importance and it further attests to the suitability of CVVH for the treatment of critically ill patients.