The purpose of the study was to evaluate the possibility of preventing delayed union in fractures by the use of low-frequency pulsing electromagnetic fields (PEMFs). The study was conducted in two parts, both with control groups. Fibular osteotomies in rats and diaphyseal fractures of the tibia in humans were treated with and without electrical stimulation (PEMF). The rats were sacrificed on the 8th and 23rd days respectively in order to evaluate the histological picture of the repair callus and its mechanical resistance. In the human subjects, the clinical and radiological follow-up took into account various factors known to affect the rate of union in the various fracture groups. The results obtained suggest that PEMF stimulation is capable of accelerating and modulating the physiological process of union by its favourable effect on osteogenesis.