1. Into osseous defects cut in the pelvis of rats, Kiel bone grafts were implanted after impregnation with the animals' own fresh bone marrow, obtained by femoral puncture. Unimpregnated Kiel bone grafts and Kiel bone grafts impregnated with an antibiotic solution were implanted as controls.

2. Histological examination of the implant area showed that in the marrow-impregnated grafts new bone formation could be observed after twelve days, and that during an observation period of 135 days after implantation bone formation occurred in thirteen out of nineteen rats. In four of these cases a continuous bony bridge developed over the defect.

3. In the unimpregnated grafts no more than a small amount of new bone was seen in only one of seven rats. In the antibiotic-impregnated grafts no bone formation was found in six rats during the same period of observation.