The effect of lesser sac drainage with or without lavage on some early predictors and on outcome in acute necrotizing pancreatitis was analysed. The evaluation was made prospectively for 24 patients, in a single centre study. According to Ranson's criteria and laparotomy findings, the lavage and drainage groups were comparable and the pancreatitis was severe and necrotizing in both groups. In a longitudinal analysis of the first 4 postoperative days, lavage did not show any advantage over drainage, as measured by seven prognostic signs (serum creatinine, blood glucose, base excess, haematocrit, white blood cells, C-reactive protein and immunoreactive phospholipase A2 concentration). Furthermore, the study did not find that lavage had any positive effect on the incidence of mortality (36 versus 17 per cent in the drainage group) or on septic complications in acute necrotizing pancreatitis. In the total series the extent of pancreatic necrosis was an essential predictor of the outcome.