To assess bone marrow lodgement of bacteria that produce osteomyelitis, 10(6) colony forming units of 16 nonhemolytic strains of Staphylococcus aureus was injected intravenously into mice. Eleven of 16 strains showed bone marrow lodgement without the death of mice. The M-138 strain induced osteomyelitis in 100% of the mice. Furthermore, the difference of compact colony forming active substance activity between bone marrow lodgement and nonlodgement strains was statistically significant. Compact colony forming active substance, which is an alkali stable polysaccharide located on the cell surface of Staphylococcus aureus strain, caused compact formation of the strains in serum soft agar or fibrinogen soft agar, and it clotted animal plasma. These results suggest that bacterial factors are important for bacterial lodgement at the onset of staphylococcal hematogenous osteomyelitis.