The quality of osteochondral repair produced by coral grafted into subchondral bone was examined. Osteochondral defects of 4 mm diameter and 4 mm deep in left femoral grooves of 24 rabbits were repaired using plugs of natural coral or left empty to heal naturally as ungrafted controls. The right knees were kept intact for normal controls. The morphology of the repair tissue, at three and six months post operation, was characterised using histology and by scanning electron microscopy. Resorption of coral and its replacement by new bone was demonstrated using Energy Dispersive X-ray Analysis (EDXA) of the scanning electron microscope. The resorbing coral was gradually replaced by bone at subchondral bone level. The surface tissue matured with time and at six months it was anatomically similar to the adjacent hyaline cartilage: it contained cells that were shaped and arranged in columns similar to the normal controls. The ungrafted controls had healed with fibrous tissue which was often markedly thicker than the adjacent hyaline cartilage and was separated from the surrounding by vertical fissures. Coral grafting of the osteochondral defect enhanced repair of surface tissue.