The activities of protein kinases C (PK-C), protein kinase A (PK-A) and other protein kinases independent of Ca(++)-phospholipid and cAMP in normal human liver and human hepatocellular carcinoma (HCC) xenograft in nude mice were determined. It was found that all the three protein kinases (PK-C, PK-A and the total "other" kinases) increased in HCC as compared with those in the normal liver. The increase was especially marked in PK-C. Its activity in cytosol was increased to 8.5 and 5.9 times as the normal values. It was also revealed that the relative content of phospholipids in the total lipid decreased in HCC. Among the constituent fractions of phospholipid, only lysophosphatidylcholine (LPC) was significantly increased both in absolute amount and its percentage in relation to total phospholipids. The causal relation between the increased PK-C activity and LPC is discussed.