Anti-ganglioside GQ1b antibody induces neuromuscular blocking on mouse phrenic nerve-diaphragm preparations. Several reports suggest that patients with this antibody show abnormal neuromuscular transmission in the facial or limb muscles, but limb muscle weakness is unusual in Miller Fisher syndrome that is often associated with anti-GQ1b antibody. To determine whether anti-GQ1b sera affect neuromuscular transmission in human limb muscles, axonal-stimulating single fiber electromyography was performed in the forearm muscle of seven patients with anti-GQ1b antibody. All showed normal jitter and no blocking. Anti-GQ1b antibody does not affect neuromuscular transmission in human limb muscles. The different findings in mouse and human may be explained by the extent of expression of GQ1b on the motor nerve terminals in the muscle examined.