OBJECTIVES: To compare the osteolytic activity of surface‐associated material (SAM) and lipid A‐associated proteins (LAPs) from periodontopathogenic bacteria. MATERIALS AND METHODS: Surface‐associated material was extracted from the surface and LAPs from the cell walls of a range of periodontopathic bacteria includingActinobocillus actinomycetemcomitansandEikenetla corrodens. These bacterial fractions were assayed to determine their composition and their capacity to induce bohe resorption was determined by use of the neonatal murine calvarial bone resorption assay.RESULTS The SAMs from E. corrodens andA. actinomycetemcomitansdemonstrated bone‐resorbing capacity at concentrations as low as I ng ml which, given the molecular weights of the active components, is in the picomolar range of activity. In contrast, the SAMs from the other three bacteria were significantly less potent and showed a lower efficacy. The LAPs all showed significant, and similar, capacities to induce bone breakdown.CONCLUSIONS This is the first demonstration that LAP from periodontopathic bacteria can stimulate bone degradation. The LAPs from diverse bacteria all produced similar levets of bone‐resorbing activity. in contrast, the SAM showed significant differences in potency and in efficacy (maximal stimulation). This may mean that in vivo certain periodontopathic bacteria have significantly more bone‐resorbing capacity than others and should be therapeu