Multifocal motor neuropathy (MMN) is a newly recognized disorder with a characteristic clinical picture. The diagnosis of MMN is established by the presence of a specific electrodiagnostic abnormality, conduction block confined to motor axons, and in some instances by the associated high titers of anti-GM1 antibodies. Clinical improvement may be achieved by treatment with intravenous immunglobulin or cyclophosphamide, which underlines the importance of recognizing these patients. We present two patients with slowly progressive predominantly distal weakness and muscle wasting of an upper extremity characteristic of MMN. Extensive electrophysiological examinations are necessary to demonstrate conduction block of motor axons, which distinguishes patients with MMN from patients with motor neuron disease. Other diagnostic possibilities are discussed.