We report a new case of neuromuscular block overlap between Myasthenia Gravis and Eaton-Lambert syndrome. A 64-year-old man with a 4-months history of gait disturbance was admitted for ophthalmoplegia worsening during exercise and decreasing at rest. Clinical examination after exercise, revealed limbs weakness and areflexia, palsy of the left eye abduction and a left ptosis. The level of anti-acetylcholin-receptor antibodies was high. Electrophysiological explorations revealed a decrement at 3 Hz and a increment at 30 Hz, with a reduction in amplitude of the initial motor potential. This patient improved under a combination of guanidine and anticholinesterase drugs. From this case and 9 previously reported cases, we propose 4 criteria for the diagnosis of such neuromuscular blocks: 1) exercising symptoms and signs, including areflexia, 2) presence of anti-acetylcholin-receptor antibodies, 3) reduction of the amplitude of the initial motor potential, with a decrement at 3 Hz, and an increment at 30 Hz, and 4) clinical and electrophysiological improvement under guanidine and anticholinesterasic drugs therapy.