['Visceral ischaemia and cytokine release are early stages in the development of shock and multiorgan failure. Because of lack of methods to measure anaerobic metabolism or visceral hypoxia in the early phase, diagnosis is not usually established until shock and organ failure are evident.', 'Nineteen patients were studied postoperatively after major abdominal gastrointestinal surgery. A microdialysis catheter was placed intraperitoneally before closure of the abdomen. Analysis of glucose, pyruvate and lactate was performed every second hour and the ratio between lactate and pyruvate was calculated. Peritoneal fluid was collected from a peritoneal drainage for analysis of tumour necrosis factor alpha (TNF-alpha) and interleukin 10 (IL-10).', 'Sixteen of the patients had a normal postoperative course; the lactate/pyruvate ratio started at the level of 20 immediately postoperatively and decreased significantly during the first 45 postoperative hours (P = 0.007). A similar pattern was recorded for peritoneal TNF-alpha, which decreased correspondingly (P = 0.003). A correlation coefficient of 0.303 (P < 0.001 ) between lactate/pyruvate ratio and TNF-alpha was found. After an initial short increase, IL-10 decreased over time (P < 0.001). Three of the patients had abnormalities in the microdialysis results, cytokines and clinical outcome. These patients are presented separately.'] Is postoperative on-line monitoring with intraperitoneal microdialysis a sensitive clinical method for measuring increased anaerobic metabolism that correlates to the cytokine response?