The direct comparison of O-alkylglycerol composition in the neutral lipids fractions prepared from human hepatocellular carcinomas with that in corresponding preparations from nonneoplastic liver is reported. Tumor-bearing liver and noncancerous liver specimens were obtained either during surgery or at autopsy. Thirty different tissue specimens obtained from 18 cases were analyzed. Representative samples from each specimen were examined microscopically to confirm the pathological diagnosis. Gas chromatographic analysis of alkylglycerol derivatives showed that hexadecylglycerol, octadecylglycerol, and octadecenylglycerol were the principal components. Compared to the noncancerous liver, hepatocellular carcinomas contained higher proportions of hexadecylglycerol and lower proportions of both C18-glyceryl ethers. Associated with this change was an increase in the proportion of saturated to monoenic alkylglycerols. These abnormalities appeared to be more severe in the necrotic areas of the tumors. Higher concentrations of neutral alkyl glycerolipids and of cholesterol were found in the tumors; no differences between the two groups could be found in the levels of ether-linked phosphoglycerides, triglycerides, and lipid phosphorus.