Open diagnostic peritoneal lavage was 97.8 per cent accurate for diagnosis of intra-abdominal injury in 2,072 blunt trauma victims. The only significant injuries missed were in certain patients with a ruptured hemidiaphragm, renal trauma and extraperitoneal bladder rupture. However, these injuries were identified by other means. False-postive lavage results are generally a consequence of technical error and can be minimized by careful surgical technique. Hemoperitoneum must be explained for all patients to prevent needless morbidity and mortality. Only diagnostic tests of proved value in blunt abdominal trauma should be used and risk to the patient must be minimized. We currently rely upon diagnostic laparotomy to evaluate hemoperitoneum in patients with a weakly positive lavage result confirmed by a second infusion. With this policy, approximately one of every four to five laparotomies was for injuries not requiring surgical therapy; and, the over-all morbidity rate and mortality was 12 and 3.5 per cent, respectively, in this group. By using open diagnostic peritoneal lavage in essentially all blunt trauma victims, we have had no deaths from either unrecognized intra-abdominal injury or delayed treatment.