A prospective study of an Intracath method of diagnostic peritoneal lavage was done of 100 patients with blunt abdominal trauma. Initial results in dogs confirmed the reliability and sensitivity of the technique. In patients, it proved to be 96 per cent accurate. Fifty-eight patients had true-positive results, and in 52 of these, subsequent laparotomy demonstrated significant hemoperitoneum and intra-abdominal injury. Six patients had intra-abdominal injuries of limited significance. Thirty-eight of these patients were considered to have true-negative results. In one patient, false-negative, signs of intra-abdominal bleeding later developed, and a splenectomy was performed without incidence. There were three false-positive results. These patients underwent laparotomy and recovered without a problem. The only complications noted were puncture of the urinary bladder in one patient and subcutaneous infusions of lavage fluid in two patients which were recognized during the procedure. Results of this study demonstrate the safety and reliability of the Intracath method of peritoneal lavage for patients with blunt abdominal trauma.