The present study was designed to investigate some role of whole blood cells in lipid metabolism compared to that of liver in acute carbon tetrachloride intoxicated rats. In order to determine this, in vitro incorporation of (14)C-acetate Na into gross lipid fractions, major lipid fractions and total fatty acids was studied. The experimental animals employed were male Wistar rats, which were subjected to subcutaneous injection of 50% CCl4 in olive oil, 0.2ml/100gm. of body weight. Animals were sacrificed at time intervals of 4 and 48 hours following treatment. The results obtained are summarized as follows: 1) (14)C incorporation by liver slices into total lipids, unsaponifiable lipids and total fatty acids was markedly decreased at 4 hours, but at 48 hours it was strikingly increased in accordance with liver cell regeneration. On the other hand, (14)C incorporation by whole blood cells into each of them showed a trend toward an increase at 4 hours, although there were few differences between carbon tetrachloride administered rats and controls at 48 hours. 2) Percent (14)C incorporation by liver slices into TG and NEFA increased significantly following CCl(4) treatment, while whole blood cells incorporated relatvely more radioactivity into NEFA than that of controls. Consequently it is considered that fatty liver would be caused by enhancement of TG and NEFA synthesis in liver, and at the same time lipid metabolism in whole blood cells would contribute to fatty liver. 3) In acute CCl(4) intoxication of rats, a decrease of percent (14)C incorporation by liver slices into fatty acid group 14:0+16:0, namely the decreased activity of malonyl CoA pathway was observed, while that into 20 carbons and more longer chains, fatty acids, formed via mitochondrial pathway, showed a significant relative increase; the results being similar to those observed with whole blood cells.