Expression of cytokeratins no. 7 and no. 19, typical of the mature biliary tract and of embryonic and fetal hepatocytes, has been evaluated in primary liver tumors from 12 children. Of 7 children with hepatoblastoma, 6 were strongly reactive for cytokeratin no. 19 and only 4 were weakly positive for cytokeratin no. 7. In contrast, the remaining tumors, including 2 hepatocarcinomas, 1 sarcoma, 1 hamartoma and 1 hemangioma were positive for cytokeratin no. 7, while cytokeratin 19 was present in 1 hepatocarcinoma and in the hamartoma. All these tumors, as well as 1 hepatoblastoma and the sarcoma, were also reactive for cytokeratin no. 8, typical of hepatic cells.