Computed Tomography (CT) is a highly accurate method of detecting and clarifying the nature of space-occupying lesions within the liver and pancreatic disease. It was found to be a reliable, non invasive method for detecting the lesion. A normal range of attenuation values were obtained from 71 CT examinations of the upper abdomen, that is liver, spleen, pancreas, aorta, before and after contrast enhancement in whom no radiologic or laboratory abnormality of these organs were detected from March to September, 1983. The results were as follows ; 1. the age distribution was from 28 years to 71 years. The sex ratio was 45 male to 26 female. 2. Mean Hounsfield Units (HU) in liver before contrast enhancement and after contrast enhancement liminute, 3 minutes, 5 minutes, 10 minutes were 56.1$pm$3.85, 75.0$pm$4.77, 82.0$pm$3.71, 84.3$pm$2.76 and 88.2 $pm$3.95 HU respectively. 3. Mean Hounsfield Units in pancreas before contrast enhancement and after contrast enhancement 1 minute, 2 minutes, 5 minutes, 10 minutes were 43.0$pm$4.30, 66.5$pm$4.27, 71.2$pm$2.39, 74.4$pm$3.00 and 79.2$pm$2.90 HU respectively. 4. Mean Hounsfield Units in spleen before contrast enhancement and after contrast enhancement 1 minute, 3 minutes, 5 minutes, 10 minutes were 53.0$pm$4.31, 71.4$pm$2.84, 75.3$pm$2.70, 80.5$pm$ 3.04 and 83.2$pm$2.14 HU respectively. 5. Mean Housfield Units in aorta before contrast enhancement and after contrast enhancement 1 minute, 3 minutes, 5 minutes, 10 minutes were 45.1$pm$5.39, 86.7$pm$6.86, 92.5$pm$5.33, 106.8$pm$4.12, and 114.1$pm$5.02 HU respectively. 6. The most significant finding was that the liver normally had the highest attenuation values of any of the organs measured. When another viscera in upper abdomen had a attenuation value gradter than that of the liver, this reflected abnormal lesions.