BACKGROUND Increased survival with high-volume continuous veno-venous haemofiltration (CVVH) has been demonstrated in critically ill patients. This may be the result of intensified blood purification or an effect on the immune system. We hypothesized that CVVH modifies the cell-mediated immunity. We investigated the effect of high-volume CVVH for 24 h on the cell-mediated immunity following endotoxin infusion. METHODS Thirty pigs were divided into three groups. Ten pigs received 30 microg/kg of Escherichia coli endotoxin. These pigs were treated with CVVH (replacement 35 ml/kg/h) over the following 24 h. Ten pigs received the same bolus of endotoxin and ten pigs served as a control group. The adhesion molecules CD18, CD44 and CD62L and the ability to respond with an oxidative burst were measured. The number of neutrophils was counted in blood and lung tissue. The lymphoproliferative response and cytokines interleukin-6 and interleukin-10 were measured. RESULTS The infusion of endotoxin was followed by initial granulocytopenia and, later, granulocytosis, activation of CD18 and CD62L, and increased oxidative burst. The cytokine level was increased. CVVH had no effect on the adhesion molecules or cytokine level and did not reduce the number of granulocytes in the lung significantly. CVVH, however, reduced the oxidative burst activity of neutrophils after 2 h of treatment. CONCLUSIONS In the first few hours after endotoxaemia, high-volume CVVH reduced the oxidative burst activity of neutrophils. However, in the long term, CVVH was unable to modify the endotoxin-induced changes in cell-mediated immunity.