Repeated haemoperfusion over activated charcoal was performed in unanaesthetized and unrestrained rats, using a specially designed system. This allowed the effects of haemoperfusion on body weight, organ weight and various biochemical and haematological parameters to be studied, without the possible influence of repeated stress and exposure to anaesthetic agents. The procedure was well tolerated, even after 4 consecutive haemoperfusions. Changes in body weight occurred, but no significant difference was noticed between animals subjected to 4 consecutive haemoperfusions and those perfused through empty columns. Organ weight of liver and spleen were comparable to control values, but kidney weight increased after haemoperfusion over activated charcoal, but not in control animals. A progressive rise in leucocyte count was found after successive haemoperfusions, but levels returned to normal 21 days after their initial operative procedure. Platelet counts fell after charcoal haemoperfusion, but returned to within normal levels before the next perfusion.