Purpose : To compare the efficacy of the split-bolus contrast media injection technique in helical CT angiography (CTA) of the whole aorta and iliac arteries with that of the single-bolus technique. Materials and Methods : Using the split bolus technique in 23 patients, 90 ml of contrast medium (Ultravist 300) was injected at a rate of 3ml/sec ; this was followed by an 8-sec pause and the subsequent injection of 30ml. Using the single bolus technique in another 23 patients, 120ml of contrast medium was injected for 40sec. continuously. CT angiography of the thoracic aorta (slice thickness/pitch = 3mm/2:1) was performed, first followed by an interscan delay of 8sec, and the abdominal aorta and iliac arteries were then scanned(slice thickness/pitch=3mm/2:1 or 5mm/1.5:1). In all patients, CT density was measured in the aortic lumen at eight levels, from the origin of the aorta to the iliac bifurcation. Results : Using the split bolus technique, visual assessment revealed second density peak in the aortic lumen of the upper abdomen in 15 of 23 patients(65%), while the use of the single bolus technique revealed no second density peak in any patient. CT density in the aortic lumen at the level of the esophagogastric junction, and at all levels below this except the abdominal aortic bifurcation, was significantly higher using the split bolus technique than with the single bolus technique (t-test, P<0.05). Conclusion : For CTA of the whole aorta and iliac arteries, the split bolus technique is more effective than the single bolus technique.