The autoimmune myasthenia gravis (AMG) in rabbits was produced by intradermal injection of N-AChR-rich membrane vesicles isolated from the electric organ of Narcine limlei. After i.v. 4-aminopyridine (4-AP) 0.8 mg.kg-1 to 8 AMG rabbits, their general posture improved promptly, the features of gastrocnemius compound action potentials and toe twitches elicited by 4-Hz stimuli applied to the sciatic nerve returned to normal, and the tetanic plateau evoked by 50-Hz indirect stimulation was again well sustained. This improved condition lasted 9.1 +/- 2.5 h. Other 8 AMG rabbits given 3,4-diaminopyridine (3,4-DAP) 0.4 mg.kg-1 showed a similar improvement for 9.3 +/- 3.1 h. These results indicated that 4-AP and 3,4-DAP were effective in treating the AMG in rabbits, they may be useful in the clinical treatment of myasthenia gravis patients.