Cytokines are a large and rapidly expanding group of polypeptides produced by many different cell types. Increasing interest has been focused on the role of cytokines as mediators of metabolic, immunological and endocrine responses to surgery. The cytokine response in patients undergoing cardiac surgery during cardiopulmonary bypass (CPB) is fairly well-defined and dominated by the proinflammatory cytokines IL-6, TNF alpha and IL-8 and the antiinflammatory cytokine IL-10. Little is known about the cytokine response in patients who develop postoperative complications but CPB with mechanical trauma and blood contact to artificial membranes is definitely an unphysiological state and may contribute to an uncontrollable response similar to that of patients with multiorgan failure and septic shock.