Electrodiagnostical studies were carried out on three patients with Wilson's disease. The motor nerve conduction velocity was low but not markedly decreased. Some values of the sensory conduction velocity were decreased; the sensory action potentials showed low amplitudes and contained large amounts of late phases. Also, the electromyogram of one female patient showed denervation in the begin of treatment. There are no indications of polyneuropathy in Wilson's disease in the literature. There have been histological reports, however, which indicated lesions of the peripheral nerves in Wilson's disease as our own electrodiagnostical findings do.