Ilisarov's idea that electrical phenomena could contribute to the efficacy of the ring fixation apparatus prompted us to carry out this preliminary investigation. Patients with lower leg fractures and a four-ring fixation apparatus were selected; the electrical potentials were measured over non-fractured and fractured bones. Patients who could not be studied in the Faraday box were subjected to great disturbances, caused by mains voltage and a neighbouring transmitter; in these cases no objective results could be obtained. Only measurements in the Faraday box yielded reproducible results. The results demonstrate that there is generally a difference in electrical potential among the four rings in patients fitted with an Ilisarov apparatus. Furthermore, weight-bearing on the fixator-bone system causes changes in the electrical potential among the rings.