This study compares effectiveness of two commercially available signals, Pulsed Electromagnetic Field (PEMF) and Combined Magnetic Field (CMF) clinical signals, to stimulate bone healing in rabbit tibial osteotomies. One millimeter osteotomies in New Zealand White rabbits, stabilized with external fixators, were exposed daily to either signal for 30 minutes, three or six hours. Osteotomized sham controls received no signal exposure. Analyses of torsional strength, periosteal callus area and fracture healing stage demonstrated dose responses to increasing daily exposures to both signals. By 14 days torsional strength increased over shams in the three and six hour-treated groups, significant only for the six hour groups (p<0.05). By 21 days both three and six hour-treated groups were significantly stronger than shams (p<0.05, p<0.005) and the PEMF 30 minute treated group also showed significance (p<0.05). PEMF versus CMF-treated groups were not different at any exposure time. Both CMF and PEMF signals were most effective in this model when used for six hours per day. In this model we demonstrate that though both PEMF and CMF are "bioactive" and promote healing at shorter and longer exposure dosages, there exists an "optimal" threshold effect of 6 hours/day electromagnetic wave stimulation for bone healing.