Electron microscopic investigation on osteogenetic process at the implant surface of threadless rod-type titanium implants with different surface roughness of Ra 0.4 +/- 0.01 microm, Sm 2.6 +/- 0.3 microm and Ra 2.0 +/- 0.12 microm, Sm 36 +/- 9.1 microm was performed at the early stage of 21 and 42 days post implantation into the jawbones of four beagles under the load bearing condition of functional mastication. The implant surfaces were covered with a blood clot and haematopoietic stem cells (HSC) including phagocytic monocytes immediately after the implantation. Successively, osteogenic stem cells (OSC) migrated from cortical and/or trabecular endosteum to the HSC-layer on the implant surface. The new bone formation at the implant/bone marrow interface was developed by collaboration of osteomediator cells (OMC) differentiated from monocytes of HSC and osteoblast phenotype cells of OSC derived from endosteum of cortical bone and/or trabecular. The new bone layer at the implant surface consisted of two layers, solution-mediated calcification layer of pseudo bone and cell (osteoblast) -mediated calcification layer of true bone. The pseudo bone was produced by solution-mediated calcification of OMC- and HSC-remnants near by the implant surface. The bone healing process at the implant/bone marrow interface depended upon two factors; the migration of OSC from cortical and/or trabecular endosteum to the implant surface and the healing potentiality. Topographic dependency upon the bone healing potential at implant/bone marrow interface was not confirmed in this experiment under the load bearing condition of functional mastication.