A retrospective study was undertaken to evaluate peritoneal lavage in detecting abdominal penetration. Two hundred thirty-five patients with thoracoabdominal, flank, or tangential abdominal gunshot wounds were lavaged. Of these patients, 44 (18.7%) had positive lavages, defined as red blood cell counts greater than 10,000 cells/mm3, white blood cell counts greater than 500 cells/mm3, or the presence of bile, feces, or vegetable matter. There were 13.6% false positives and 1.0% false negatives, with an overall accuracy of 96.6%. The results were unaffected by mechanism or site of injury. If the criteria were changed to include red blood cell counts greater than 100,000 cells/mm3, there would have been no false positives, but an unacceptably high 11.1% false negative rate. Therefore we conclude that peritoneal lavage can be a reliable indicator of abdominal penetration provided sufficiently sensitive criteria are used. These criteria should include red blood cell counts greater than 10,000 cells/mm3 instead of 100,000 cells/mm3.