Leucocyte activation and proinflammatory cytokine release (tumour necrosis factor (TNF) and interleukin 6 (IL-6)) are thought to contribute to the induction of a systemic inflammatory response, an acute-phase response and multiple organ failure in patients with acute pancreatitis. The serum concentration of TNF, soluble TNF receptors (sTNFR55 and sTNFR75), IL-6 and C-reative protein (CRP) in 58 patients with acute pancreatitis was assessed during the first 2 days of admission. Thirty patients had mild disease and 28 severe disease, of whom 18 developed local pancreatic complications alone (Atlanta classification) and ten developed organ failure (a Goris score of 1 or more). TNF was detected in only 17 patients on the first day of admission, while soluble TNF receptors were detected in all patients and IL-6 in 34. On the first and second days of admission there was a progressive and significant (P < 0.03) increase in the median concentration of sTNFR55, sTNFR75 and IL-6 in patients eventually classified into those with mild disease, a local pancreatic complication alone, or organ failure. This pattern was also evident in CRP levels from the second but not the first day of admission. These findings suggest that proinflammatory cytokines or their soluble receptors may be more accurate early predictors of outcome than CRP, Moreover, markers of inflammation in the sera of patients with acute pancreatitis are highest in those who subsequently develop organ failure.