In this study the extraction and the immunochemical features of a lipopolysaccharide-like (LPSL) macromolecule of T. denticola strains 35405, 35404, 33521 and 11 were investigated. The yield of LPSL molecule ranged between 0.5-0.9% of the cell dry weight, it possessed Limulus amebocyte lysate clotting activity, and it contained glucosamine, phosphate, heptose, glucose, small amounts of KDO, myristic and beta hydroxy myristic acid. Sera obtained from healthy individuals (ADA type I) periodontitis, from 3-8 month old infants, or the mouse monoclonal antibody, diluted 1:2, against T. pallidum did not react with the LPSL antigens of T. denticola strains 35405, 35404, 33521, and 11. Sera from patients with ADA type III-IV periodontitis were reactive with two 8-14 kDa bands even at serum dilutions of 1:2000. Sera from patients with ADA type II periodontitis showed good antibody response to the 8-14 kDa band at a dilution of 1:50, but were weekly reactive, or nonreactive at serum dilutions of 1:200. This study indicates that extraction of a lipopolysaccharide-like macromolecule is feasible from the assay spirochetes, and this macromolecule may be used as an antigen for the diagnosis of ADA types II-IV periodontitis.