We studied the role of bone-marrow reconstituted porous ceramics in enhancing healing of a 5-mm femoral diaphyseal defect fixed with a rigid polyethylene plate in rats. Osseous repair was evaluated by histologic scoring. When blocks of porous calcium phosphate ceramics alone were introduced into the defects, most cases showed fibrous tissue interposition at the host bone-ceramic junction 1 month after implantation, and only four of 12 defects developed osseous or osteochondral union at both the proximal and distal junctions 2 months after surgery. However, when the ceramic was combined with syngeneic viable marrow cells, new bone formation occurred in isolated pore regions of the ceramic at 1 month, and extensive bone formation was seen in most pore regions 2 months after implantation. Out of 12 implants, complete bone union was seen in eight, and one showed osseous or osteochondral union at both junctions 2 months after surgery. Our results indicated that composite grafts of porous calcium phosphate ceramics and marrow cells may be clinically applicable to enhance osteogenesis and osteoconduction.