Intensive insulin therapy, aiming for strict normoglycaemia, is associated with increased survival in critically ill patients. Insulin therapy concomitantly reduces plasma-free fatty acids. Recent studies indicate that free fatty acids mediate inflammation. In addition to plasma glucose and free fatty acid-lowering effects, insulin also has anti-inflammatory properties. This study was designed to study the pro-inflammatory effects of two free fatty acid concentrations during acute endotoxaemia and controlled comparable levels of plasma glucose and insulin. Twenty pigs were anaesthetized and mechanically ventilated. Pigs were randomized to two different, constant Intralipid (R) infusion rates, throughout observation. All pigs were administered continuous intravenous infusion of endotoxin and subjected to controlled levels of p-glucose (4.5 mmol/l) and insulin by use of a hyperinsulinaemic euglycaemic clamp. Changes in circulating tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, leucocytes, insulin, glucose, free fatty acids, triglycerides, albumin, blood gases, temperature, and, haemodynamic function were monitored. Immediately following killing, biopsies were taken from heart and kidney. Biopsies were analysed for protein content of TNF-alpha, IL-6, IL-8 and IL-10. Sustained elevated and significantly different plasma levels of free fatty acids were demonstrated between groups (mean free fatty acid concentrations, 1.62 mM versus 0.58 mM, p < 0.0002). Endotoxaemia induced a steep increase in plasma TNF-alpha, IL-6 and leucocytes, however, without differences between the low- and high-free fatty acid groups. Cytokine content in heart and kidney tissue was not modified by free fatty acids. Compared with the response obtained at lower free fatty acid levels, high free fatty acid levels did not exacerbate the inflammatory response to acute endotoxaemia. Our results do not support the role of free fatty acids as a significant pro-inflammatory mediator.