The present invention relates to monoclonal antibodies to advanced glycosylation endproducts formed in vivo and cross-reactive with advanced glycosylation endproducts formed in vitro, and to methods of diagnosis and therapy based thereon. More particularly, the invention is directed to a monoclonal antibody, or an antigen-binding fragment thereof, reactive with in vivo produced advanced glycosylation endproducts (AGEs), which monoclonal antibody or antigen binding fragment thereof demonstrates an immunological binding characteristic of monoclonal antibody 4G9 as produced by hybridoma 4G9, deposited with the American Type Culture Collection (ATCC) and assigned Accession Number CRL 11626, on Apr. 27, 1994. In a specific embodiment, the 4G9 antibody is used in a sandwich ELISA to detect ApoB-AGE, IgG-AGE, collagen-AGE, serum-AGE peptides and proteins and urinary-AGE peptides and proteins.