BCA-225 is a glycoprotein identified in human breast carcinoma cells that has been reported to show a restricted distribution in other human tissues. To further define the presence of BCA-225 in human carcinomas, the authors performed an immunohistochemical study, applying a commercially available monoclonal antibody to BCA-225 to formalin-fixed, paraffin-embedded sections of 446 adenocarcinomas from a variety of sites. BCA-225 expression was found to be common in adenocarcinomas of the breast (98%), kidney (94%), ovary (80%), and lung (74%) but was infrequent in adenocarcinomas of the gastrointestinal tract (10-16%). Adenocarcinomas of the prostate, bile ducts, thyroid, endometrium, endocervix, and pancreas showed an intermediate frequency of BCA-225 expression (36-68%). Although rare tumor cells in three hepatocellular carcinomas showed reactivity for BCA-225, staining of more than 10% of the tumor cells was not seen in any of the 23 hepatocellular carcinomas that were studied. The authors conclude that BCA-225 is expressed commonly in human adenocarcinomas and that it is not a breast-specific antigen. Antibodies to BCA-225 may have utility in helping one to exclude hepatocellular carcinoma in certain clinical settings.