From January through December 1990, a prospective study comparing the accuracy of diagnostic peritoneal lavage (DPL), abdominal computed tomographic (CT) scanning, and abdominal ultrasonographic (US) scanning was carried out. Patients with stable vital signs following their initial resuscitation coupled with equivocal physical examination findings received both CT and US scanning. A DPL was then done. If any of these three examinations produced positive findings, a laparotomy was done and the surgical findings were compared with the results of the diagnostic studies. Fifty-five patients were studied (44 men, 11 women), with a mean age of 43 years and a mean ISS of 18.5 +/- 10.5. The sensitivity, specificity, and accuracy were 100%, 84.2%, and 94.5% for DPL, 97.2%, 94.7%, and 96.4% for CT scanning, and 91.7%, 94.7%, and 92.7% for US scanning. Problems do exist in identifying isolated small intestinal perforations with ultrasonography. Since more and more trauma centers are using ultrasonography in the emergency department as a screening method in the management of patients with blunt abdominal trauma, it is important to avoid overestimating its capability. Frequent re-evaluation of the patient's condition, repeat ultrasonographic scans, diagnostic peritoneal lavage, and CT scanning are complementary and important in the diagnosis of blunt abdominal trauma.