In four patients who received periocular injections of botulinum toxin for blepharospasm, abnormal neuromuscular transmission was demonstrated by single-fiber EMG in arm muscles. The time course with which the abnormalities developed and cleared, as well as the inverse relationship between the neuromuscular jitter and the firing rate in the abnormal muscles, indicated that the toxin caused the abnormalities in arm muscles. No weakness was detected clinically in muscles distant from the face, but the abnormal neuromuscular transmission indicates that the toxin spread remotely from the site of injection.