Monolayer cultures were established from explants of muscle obtained from 6 patients with Duchenne muscular dystrophy (DMD) and 9 controls. Electrophysiological studies were made after 3-4 weeks in vitro, when many myotubes had formed. An intracellular electrode was used to record cell membrane potential, and acetylcholine was applied by ionophoresis. The myotubes grown from Duchenne muscle showed greater acetylcholine sensitivity than controls.