This study evaluated the effect of pulsed electromagnetic fields (PRFM) on the helaing of lumber spinal fusions. Bileteral posterior facet fueions were performed at L1–2 and L4–5 in 24 adult mongral dogs. Ager surgery, eitght animals were stimulated with a pulse burst hype signal (PEMF) for 30 minutes a day, and eight animals were stimulated with the smae PEMF for 60 minutes a day. The remaining eight animals received no active PEMF stimumations and served as controls. Four animals from each gruop were euthanatized at 6 and 12 weeks, and the facet fuslons were evaluated using high resolution radiographs and routine histology. No statistical differences in the rediographic or histologic appearances of the fusion mass could be detected between the stimulatee and c ontrol groups at either 6 or 12 meeks. The results of this study suggest that PEMF stimulation had no effect on the healing of the primary posteior splnal.