Excessive leukocyte activation has been proposed as a key mechanism in the onset of acute pancreatitis. In this study, we assessed the systemic release of various inflammatory mediators and tried to identify differences between patients with mild and severe disease. In a prospective study, 19 patients admitted for severe acute pancreatitis were compared with 24 patients with mild pancreatitis. Serum levels of interleukin-6 (IL-6), IL-8, and IL-10 were determined at the time of admission, and on days 1, 2, and 5 after hospitalization. Severity of pancreatitis was determined according to the Atlanta criteria. IL-6 levels peaked on admission in both groups with significant differences (p < 0.05) from days 0-2. IL-8 levels increased from day 0 in severe cases, and from day 1 in mild cases, to reach a plateau between days 2 and 5; significant differences were observed on days 0 and 1. IL-10 was highest on day 0; it decreased rapidly in mild cases but stayed significantly higher from days 1 to 5 in severe cases. These findings provide new evidence on the role of mediators of the inflammatory/antiinflammatory balance in acute pancreatitis. These molecules appear to be valuable early markers of severity.