Hybridomas secreting monoclonal antibodies specific for nonenzymatically glycated albumin were produced by fusion of SP2/0 myeloma cells with spleen cells from BALB/c mice immunized with unreduced nonenzymatically glycated albumin prepared from human plasma. Wells containing hybridomas secreting antibodies against glycoalbumin were identified by binding, in an enzyme-linked immunosorbent assay, to glycoalbumin isolated from human plasma or to albumin that had been glycated in vitro. The colony designated A717, which secreted antibodies discriminating between glycated versus unglycated albumin, was cloned four times by limiting dilution and used for further study, performed with monoclonal antibody purified from mouse ascites fluid. Specificity of A717 was demonstrated by immunoblotting and by ELISA, wherein the monoclonal antibody reacted preferentially with glycated albumin but insignificantly with unglycated albumin. Immunoblotting of human plasma with A717 on nitrocellulose yielded a single band, the electrophoretic mobility of which corresponded with that of authentic glycated albumin, indicating site specificity for glycated epitopes residing in albumin but not in other nonenzymatically glycated serum proteins. A717 differs from other antibodies raised against glycated albumin and other proteins, which recognize glycated residues only after reductive conversion to glucitol-lysine and which do not discriminate between different glycated proteins. Thus, this report describes the establishment of the first hybridoma secreting monoclonal antibody raised against unreduced glycated albumin, which is the physiologic form occurring in vivo, and for the epitope when it resides in albumin but not other proteins.