The developed enzyme linked immunosorbent assay (ELISA) was used to analyse in a pilot study the serum of subjects with periodontitis (n = 26), subjects with periodontitis and type 2 diabetes mellitus (n = 15), and healthy individuals (n = 13) for immunoglobulin (Ig)G- and IgM-antibody titres against FimA. The gene discussed is CD40LG; the disease is diabetes mellitus.