SUMMARY: The pathogenesis of postoperative hypoalbuminaemia remains a controversial and poorly understood topic. In the present study the changes in the plasma albumin level following laparotomy have been investigated by immunological methods and correlated with the concentrations of extravascular albumin in the operation wound site and in the liver. There was a fall in the plasma albumin level, accompanied by an increase in the extravascular albumin concentration at the laparotomy wound site, with no alteration in the concentration of albumin in the liver. This work confirms that postoperative hypoalbuminaemia is due to accumulation of albumin in the wound site. Increased capillary permeability is suggested as a cause of the excessive loss of plasma albumin into the surgically injured site. The role and subsequent fate of the extravascular albumin in the wound area are also discussed.