The double-step technique of repetitive nerve stimulation was compared with repetitive nerve stimulation to a distal and a proximal muscle and with single fiber needle electromyography in 10 patients with myasthenia gravis. We conclude that the double-step technique is slightly more sensitive than repetitive nerve stimulation to a proximal muscle but only 60% as sensitive as single fiber electromyography in demonstrating abnormal neuromuscular transmission in myasthenia gravis.