After giving whole-body irradiation of 600R, albumin complexed-palmitic acid-1-(14)C or linoleic acid-(14)C were used to mice, and we studied differences in changes of metabolism in these irradiated animals. For this study we messured amounts of (14)CO(2) exhaled, specific activity of liver lipids, and activities of individual fatty acid fractions with lapse of time, and obtained the following results. 1) It was found that the incorporation of palmitic acid-1-(14)C into (14)CO(2) was increased about 150% in the irradiated group as compared with that in controls. In contrast, that of linoleic acid-1-(14)C was decreased by about 50% as compared with controls. 2) The incorporation of palmitic acid-1-(14)C into liver lipids was considerable in the early stage after the the irradiation, but it decreased rapidly and became less than that of controls within a short period of time. The uptake of linoleic acid-1-(14)C into the liver of inadiated qroup was found to have been decreased. 3) In the irradiated groups, data revealed an inhibitory effect on unsaturation and chain elongation of both palmitic acid and linoleic acid.