This work investigates differences in contrast enhancement of the aorta, portal vein and liver by two different concentrations of contrast materials using an automatic bolus tracking technique. Seventy patients were assigned randomly into one of two groups. Contrast materials with iodine concentrations of 300 and 370 mg/ml were administered to patients in groups A and B, respectively. The total iodine load (600 mg/kg) and injection time (30 s) were identical. Differences in the increase of the Hounsfield unit of the aorta, portal vein and liver between the two groups were examined by t-test. There were no significant differences between the two groups in any of the contrast enhancements of the aorta, portal vein and liver parenchyma at all phases, except for enhancement of the portal vein at the late arterial phase. Females showed better contrast enhancement of the aorta and portal vein than males. With the same iodine dose and injection time, the concentration of contrast materials did not seem to influence the efficacy of contrast enhancement of the aorta, portal vein and liver, except for the portal vein at the late arterial phase. Planning of protocols for contrast media injection may be made irrespective of the iodine concentrations.