Purpose of the present study was, to proof whether homologous recombinant GH has an stimulating effect on bone healing in distraction osteogenesis. Therefore the left tibiae of 20 micropigs were osteotomized and distracted over an external fixator 2 mm daily on each of ten consecutive days. Animals were sacrificed after a healing time of another ten days. The treatment group received 100 micrograms r-pGH per kg bodyweight per day. After sacrifice, the regenerates were embedded undecalcified and cut into 6 microns thick sagittal oriented slices. Callus area, bone area, cartilagee area and bone perimeter in the regenerates were measured using an image analysis system. The results revealed, that GH promotes bone formation and maturation of the regenerate without disturbing the callus structure.