To confirm the accuracy of guided percutaneous aspiration (GPA) in distinguishing sterile from infected pancreatic necrosis, we have performed Brown-Brenn tissue Gram stains on pancreatic and peripancreatic necrotic tissue removed operatively in 15 patients. In eight patients judged to have sterile necrosis on the basis of negative cultures of pancreatic exudate obtained first preoperatively (by GPA) and then intraoperatively, necrotic tissue debrided at surgery was also free of bacteria. In seven patients judged to have infected necrosis on the basis of positive cultures of pancreatic exudate obtained first preoperatively (by GPA) and then intraoperatively, necrotic tissue debrided at surgery harbored a considerable number of bacteria. We conclude that GPA targeted to areas of necrosis accurately distinguishes infected necrosis from sterile necrosis, and in infected necrosis, the solid necrotic tissue as well as the fluid component contains bacteria. We therefore believe that infected necrosis is not likely to be eradicated by catheter drainage and should be treated by surgical debridement.