Of 147 patients with fractures of the tibia, femur and humerus, in whom an average of 3.3 operations had failed to produce union, all were treated with external skeletal fixation in situ and pulsed electromagnetic fields (PEMFs). Of the 147, 107 patients united for an overall success rate of 73%. Union of the femur occurred in 81% and the tibia in 75%. Only five of 13 humeri united. Failure to achieve union with PEMFs was most closely associated with very wide fracture gaps and insecure skeletal fixation devices.