PURPOSE: To determine the degree and effect of contrast enhancement of the hepatic parenchyma according to different injection rates, amounts and types of contrast materials. MATERIALS AND METHODS: A total of 270 patients were divided into nine groups. Each group received different volumes(120, 130, or 140ml) and was scannedwith different injection rates of 2, 3 or 4 ml/sec. Three kinds of contrast materials(Ultravist 370, Iopamiro 370, Optiray 320) were used. Hepatic enhancement was measured by comparing quantitative regions of interest(ROI) beforeand after bolus injection of contrast material which were evaluated on arterial, portal and delayed phase duringdouble spiral scanning. RESULTS: There was no significant statistical difference in contrast enhancement between the three kinds of contrast materials. In noncirrhotic patients, hepatic enhancement was greatest on portal phase and was greater at a rate of 4ml/sec than 2ml/sec or 3ml/sec on arterial phase. At the same injection rate, thevolume of contrast material was an important factor on portal and delayed phase. In the cirrhotic patients, Child's C showed more delayed peak enhancement than did Child's A. CONCLUSION: The important factors in contrast enhancement were injection rate on arterial phase and volume on portal and delayed phase. The optimal choice mustbe made after considering intrinsic variables ; in addition, our results are helpful for determining enhancement protocol during double spiral CT scanning.