Plasma membranes (PM's) were isolated from primary hepatomas induced in Wistar rats by 3'-methyl-4-dimethylaminoazobenzene, from nonhepatomal regions of the same rat livers, and also from various normal rat livers, including the resting and regenerating livers of adult rats and developing livers of postnatal rats. Phospholipid analyses of these PM preparations revealed the following differences in the hepatoma PM in comparison with those of the PM of normal adult resting livers: (a) decrease in the content of total phospholipids; (b) large increase in plasmalogen content; (c) relative increase of sphingomyelin and ethanolamine phospholipids, and the decrease of choline phosphoglycerides, i.e., decrease of the ratios of choline phosphoglycerides to choline phosphosphingoside and of choline-containing phospholipids to ethanolamine-containing phospholipids; (d) decrease in phosphatidylserine and phosphatidylinositol. The phospholipid composition of the PM's from normal growing livers showed definite decreases in phosphatidylserine and sphingomyelin and increases in ethanolamine phospholipids; however, no significant alteration was observed in plasmalogen content in comparison to the PM of normal adult resting livers. The PM from the nonhepatomal regions of the hepatoma-bearing livers did not show those differences observed in hepatoma PM.