The chemical composition and classical biologic activities of lipopolysaccharide (LPS; phenol-water) and endotoxin (butanol-water) preparations from virulent Treponema hyodysenterinae and avirulent Treponema innocens were examined. The LPS and endotoxin preparations from T. hyodysenteriae B204 contained approximately 80.9 and 35.2% hexose, 0.12 and 0.45% thiobarbituric acid-reactive compound, and <1 and 11.3% protein, respectively. The LPS and endotoxin preparations of T. innocens B1555a contained approximately 56.3 and 37.8% hexose, 0.45 and 0.4% thiobarbituric acid-reactive compound, and <1 and 26% protein, respectively. A silver-stained 7.5 to 15% sodium dodecyl sulfate-polyacrylamide gel showed four bands for the T. hyodysenteriae preparations, while the T. innocens preparations failed to resolve into discrete bands on electrophoresis. We determined by the Limulus amebocyte lysate assay that the treponemal preparations had comparable amounts of endotoxin activity when Eschenichia coli LPS was used as a standard. The 50% lethal doses of LPS and endotoxin from T. hyodysenteriae for BALB/cByJ mice were 380 and 80 ,ug, respectively. The treponemal preparations were poor adjuvants, failed to induce a dermal Shwartzman reaction, and were not pyrogenic. The treponemal LPS preparations, unlike the endotoxin preparations, were not mitogenic for murine spleen cells. Differences in virulence between the two treponemal species could not be associated with the biologic activities of the respective LPS or endotoxin moieties, but the endotoxin preparations were consistently more active than the purified LPS preparations. Lipopolysaccharide (LPS) is a molecule that is found in the outer membrane of gram-negative bacteria and is associated with numerous biologic effects on the mammalian immune system (25). These responses include B-cell mitogenicity, polyclonal antibody induction, adjuvanticity, macrophage activation, immunogenicity, pyrogenicity, lethality, induction of tolerance, and inflammatory reactions (25, 33, 34, 39). Different extraction methods for LPS have been reported (5, 8, 24, 46). LPS, when free of contaminating protein, is extracted by the hot phenol-water method of Westphal and Jann (46). Endotoxin preparations, which consist of LPS as well as lipid A-associated protein(s), is extracted by either the trichloroacetic acid methods of Boivin and Mesrobeanu (5) and Staub (36) or the butanol-water method of Morrison and Leive (24). Endotoxin possesses all of the aforementioned biologic activities and the ability to stimulate lymphoreticular cells from LPS-hyporesponsive C3H/HeJ mice (10, 45). This stimulation has been shown to reside with the protein moieties that are associated with endotoxin (10, 23, 25). In comparison with the LPS from Escherichia coli, there are numerous gram-negative organisms which have LPS with various chemical and biologic characteristics (12, 31, 35). These differences include the inability to detect the presence of 2-keto-3-deoxyoctonate (KDO) (9), differences in fatty acid composition ...