OP-1 (800 microg) or DBM (1900 mg) were implanted in a rabbit tibial distraction model, and healing was compared to a non treated control group. The limbs were harvested after ten weeks and examined using radiography, computerized axial tomography and histological analysis. Neither of the treatments showed a changed healing pattern. Densities as measured by CT scan were not increased and the only significant finding was an increased area of bone formation in the DBM treated group (65% increase as compared to the OP-1 group). These experimental results do not show an effect of these substances in this model of bone lengthening. They indicate that further studies are warranted to understand the process of bone formation and the working mechanisms of substances that potentially trigger bone healing.