Relatively scant chemical information has been available on the proteinases and peptidases of spirochetes in spite of the association of spirochetes with several serious infections known to plague humans and other animal species. This situation has partly resulted from difficulties in growing some spirochetes under laboratory conditions. The cells of Treponema denticola, a spirochete suggested to be associated with periodontal infections, have turned out to be a good source of new chemical information on those enzymes. Latest studies suggest that the outer cell envelope or the periplasmic space of T. denticola contains several novel proteinases and peptidases (hence called "ectoenzymes") which may contribute to the chronicity of periodontal infections. Some of the oligopeptidases discovered are specific for proline-containing host tissue peptides such as substance P, bradykinin, neurotensin, etc., and possibly small collagen fragments. The only spirochetal peptidases purified to give a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis have been obtained from T. denticola. One particular peptidase, suggested to be similar to the oligopeptidase B (EC 3.4.21.83) of Escherichia coli seems to be present in the cell envelope or in the periplasmic space at quite large concentrations. The presence of this and several other peptidases in the outer cell structures of the treponemes suggests that such enzymes are important for the nutrition of these highly motile and invasive organisms. The biological role of these enzymes can thus be envisaged in the peptidolytic processing of host tissue proteins and peptides to gradually smaller molecules to fulfill the nutritional requirements of these organisms. Although the genetic similarity between T. denticola and some other treponemes and spirochetes can be hotly debated, it is nevertheless now possible to use T. denticula enzymes as suitable objects for comparison when the chemistry of other spirochetes is studied.