We performed 92 computed tomography-guided percutaneous needle aspirations of pancreatic inflammatory masses in 60 patients suspected of harboring pancreatic infection. Thirty-six patients (60%) were found by Gram stain and culture to have a total of 41 separate episodes of pancreatic infection. Among 42 aspirates judged to be infected by computed tomography-guided aspiration, all but one were confirmed by surgery or indwelling catheter drainage. Among 50 aspirates judged to be sterile, no subsequent evidence of infection was found. All patients tolerated the procedure well and no complications were noted. As a result of this technique, we observed that pancreatic infection occurs earlier than has been previously appreciated (within 14 days of the onset of pancreatitis in 20 of the 36 patients) and that infection may recur during prolonged bouts of pancreatitis. We conclude that guided aspiration is a safe, accurate method for identifying infection of the pancreas at an early stage.