To investigate the possible expression of the carcinoembryonic antigen (CEA) gene family products on lymphoid cells, we screened 28 human cell lines derived from malignant lymphoid cells for reactivity with monoclonal antibodies (MAbs) against CEA and nonspecific cross-reacting antigen (NCA), which is one of the CEA gene family members. Six cell lines (four B cell lines and two non-T, non-B cell lines) were found to react, by a membrane immunofluorescence test, with an MAb, F34-187, which recognizes an antigenic determinant shared between CEA and NCA. None of the 15T cell lines was reactive with any MAbs tested. A glycoprotein antigen isolated with F34-187 from the cell surface showed an apparent molecular mass of ca 140 and 70 kDa in the glycosylated and deglycosylated forms, respectively, and was unreactive with MAbs specific for CEA or NCA, suggesting that the antigen is a new member of the CEA gene family.