Tumour necrosis factor (TNF) is an early mediator of sepsis and multiple organ failure; increased concentrations in serum are also observed in acute pancreatitis. In the present study the predictive value of TNF and C-reactive protein (CRP) concentrations on admission were compared in order to differentiate complicated cases of acute pancreatitis from the mild course in 77 patients. Serum TNF concentration exceeded the detectable level only in seven of 77 patients (9 per cent), although complicated pancreatitis developed in 18 (23 per cent). The sensitivity and overall accuracy of TNF concentration in predicting severe disease were only 16 and 74 per cent respectively. The corresponding values for CRP (concentrations greater than 100 mg/l) were 84 and 74 per cent respectively. These data suggest that, in contrast with CRP, the early determination of peripheral blood TNF concentration is of no clinical value in assessing the severity of acute pancreatitis.