Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disorder characterized by reduced acetylcholine release at the neuromuscular junction. We report a model of the disease developed by active immunization of rats with purely cholinergic nerve terminals (synaptosomes) isolated from the Torpedo electric organ. Electromyographic studies of neuromuscular transmission in these rats showed a weak initial response followed by a pronounced incremental response to paired supramaximal stimuli (8 msec apart). There was no such response in control rats. There was no evidence of a postsynaptic transmission deficit in the synaptosomes immunized rats. We conclude that immunizing rats with Torpedo cholinergic nerve terminals causes a specific presynaptic dysfunction and may serve as a model for the study of LEMS.