The neural-cell adhesion molecule (N-CAM) consists of three major types of polypeptides (180, 140, and 120 kDa) whose predominant differences exist within the transmembrane and cytoplasmic domains. In this study, we generated a monoclonal antibody, termed SZK1, reactive to feline CD56 (fCD56) molecules (140 kDa form of N-CAM) expressed by the baculovirus expression system and investigated fCD56 expression in feline lymphoid cells. In flow cytometric analysis, SZK1 was reactive to a feline T-lymphoblastoid cell line MYA-1. Further, SZK1 was reactive to a very small population (1.1-1.7%) of freshly isolated peripheral blood lymphocytes (PBLs) of three specific pathogen-free cats, and the reactivity was increased by culturing of PBLs in the presence of interleukin-2 following concanavalin A-stimulation (>10%). In immunoblotting analysis, SZK1 detected an approximately 160 kDa antigen from MYA-1 cells, while from RNA of the cells reverse transcription-polymerase chain reaction amplified the fragment resembling 140 kDa form of N-CAM. These finding suggest that fCD56 has similar characteristics with human CD56.