Aberrant glycosylation of mucins on the surface of adenocarcinomas leads to exposure of novel tumor-associated epitopes potentially recognizable by the immune system. Monoclonal antibodies (mAbs) have been developed against some of these epitopes. One such mAb, denoted CC49, recognizes the tumor-associated glycoprotein TAG-72. Most adenocarcinomas, including breast, colon, ovarian, prostate, and gastric, express some form of this molecule, recognizable by the CC49 antibody. The widespread distribution of the antigen on transformed cells makes the CC49 mAb a potentially powerful tool in numerous immunotherapy contexts. In the course of our studies with CC49 and certain of its molecularly engineered derivatives, we screened a number of human hematopoietic cell lines for TAG-72 expression by flow cytometry using CC49. We found that the T-cell line, Jurkat, had a higher level of CC49 mAb binding than any of the carcinoma cell lines previously evaluated in our laboratory. In addition, the myelomonocytic cell line Tf-1 and the erythroleukemia cell line K562 were also positive for CC49 mAb binding by flow-cytometric analysis. However, peripheral blood lymphocytes and certain other hematopoietic cell lines were not able to bind the CC49 mAb. Immunoblot analyses of cell extracts from the CC49 reactive lines indicated distinct protein species reactive with the CC49 antibody. In some instances, cells expressing these reactive proteins were susceptible to antibody-dependent cellular cytotoxicity using a chimeric derivative of the CC49 antibody. These results indicate that the cell membrane expression of molecules recognized by CC49 extends beyond adenocarcinomas to certain cell lines of hematopoietic origin.