In this study the authors assessed plasma leukaemia inhibitory factor (LIF), interleukin 6 (IL-6) and soluble IL-6 receptor (sIL-6R) concentrations in 28 patients undergoing coronary artery bypass graft (CABG) with extracorporeal circulation (ECC). Plasma IL-6 levels increased during ECC, reaching a 33-fold increase 6 h after surgery as compared to pre-operative values. In contrast, plasma sIL-6R and LIF concentrations did not vary significantly during cardiac surgery. Thus, LIF is not implicated in the haematological changes and in the inflammatory syndrome observed after CABG. Despite the fact that LIF and IL-6 exhibit several common biological activities, the production of these two cytokines is differently regulated during cardiac surgery with ECC. Plasma IL-6 levels increased during cardiac surgery while sIL-6R levels did not changed. These data contrast with the decreased sIL-6R concentrations with concomitantly high IL-6 levels in patients with sepsis syndrome suggesting that inflammatory reactions in sepsis and after cardiopulmonary bypass are triggered by different mechanisms.