Electrical parameters were optimized for induction of the fusion of protoplasts formed from two auxotrophic (leu−, ade−) Mucor circinelloides strains. These proved to be a pulse voltage of 66 V, a pulse duration of 66 us and six pulses at intervals of 1.0 s. Nutritionally complementing colonies were obtained at an average frequency up to 12.4%, which is substantially higher than achieved earlier with the PEG-Ca2+ method.