Sepsis is still a major cause of postoperative morbidity and mortality. Numerous biochemical indicators have been evaluated regarding their potential in predicting prognosis in sepsis. Generally, one must differentiate between indicators: those for preoperative risk of lethal sepsis, those for early prediction of lethal outcome and those for evaluating effectiveness of therapy. In the past, immunomodulatory therapies developed in various animal studies failed to be successful in humans. It has been proposed that present models have to be reevaluated, and new, clinically more relevant models should be evolved. This article will give a short overview on the most common animal models and a comprehensive overview on markers for sepsis in animal models and clinical studies. The focus will be on abdominal sepsis with a mortality rate up to 80 percent after major surgery. Two animal models designed to closely mimic the clinical course of intra-abdominal sepsis, will be compared. Furthermore, relevant clinical parameters for predicting prognosis before and after major visceral surgery are illustrated.