Onychomycosis, most commonly caused by two species of dermatophyte fungi--Trichophyton rubrum and Trichophyton mentagrophytes--is primarily treated with regimens of topical and systemic antifungal medications. This study was undertaken to evaluate in vitro the efficacy of low-voltage direct current as an antifungal agent for treating onychomycosis. Agar plate cultures of T rubrum and T mentagrophytes were subjected to low-voltage direct current electrostimulation, and antifungal effects were observed as zones in the agar around the electrodes lacking fungal growth. Zones devoid of fungal growth were observed for T rubrum and T mentagrophytes around anodes and cathodes in a dose-dependent manner in the current range of 500 microA to 3 mA. Low-voltage direct current electrostimulation has great clinical potential for the treatment of onychomycosis and perhaps other superficial maladies of fungal etiology.