Ultrasonography has been used as an investigation in patients with abdominal signs after blunt injury. Thirty-two patients were examined, of whom 11 had abnormal findings. Free intraperitoneal fluid was demonstrated in eight cases, seven of whom had this confirmed at subsequent laparotomy. The 21 patients with normal scans did not require abdominal intervention. It is suggested that ultrasonography is a reliable method of detecting haemoperitoneum and offers a valuable non-invasive method of investigating blunt abdominal injuries. The hepatorenal pouch is the site where free intraperitoneal fluid can be most easily demonstrated.