Immunocytochemistry has indicated that, in the liver, the bcl-2 gene is generally expressed in bile duct cells and tumors of biliary origin. Both in situ hybridization and immunocytochemistry were used to analyze the expression of bcl-2 messenger RNA (mRNA) and its protein product (Bcl-2) in the tissue of 50 pure primary liver tumor (PLT) specimens including 40 hepatocellular carcinoma (HCC) specimens and 10 cholangiocellular carcinoma (CC) specimens. The phenotype of the tumors expressing bcl-2 was confirmed by immunocytochemical assessment of the cytokeratin (CK) profile (CK8, CK18, CK7, and CK19). Whereas positive immunoreaction with the anti-Bcl-2 MoAb was revealed in only 8 (20%) of 40 HCC specimens and 1 (10%) of 10 CC specimens, high contents of bcl-2 mRNA were found in 26 (65%) of 40 HCC specimens and 9 (90%) of 10 CC specimens. Regarding the CK profile, only 25 (62%) of 40 HCC specimens showed pure hepatocytic lineage (CKs 8-18), whereas among the remaining 15 HCC specimens, positivity for either CK7 (12 specimens) or CK19 (5 specimens) was observed. All 10 CC specimens stained with CKs 8-18-19, and 8 of 10 stained with CK 7 as well. These results indicate that PLTs display a greater expression of bcl-2 mRNA than of the Bcl-2 protein. Furthermore, CK profile assessment confirmed that bcl-2 expression is not confined to liver tumors of biliary origin. In the absence of a well-demonstrated post-transcriptional control of the gene, the authors propose the detection of bcl-2 mRNA by in situ hybridization as a possible alternative method for assessing the expression of bcl-2 mRNA in PLT.