The analgesic effects of lidocaine and tocainide on trigeminal neuralgia have been established. However, both drugs are unpractical: lidocaine can only be used intravenously, and tocainide may exhibit serious haematological side effects. Mexiletine, a structural analogue of lidocaine that can be safely administered by the oral route, was given, as the sole drug, to four patients with active trigeminal neuralgia. After at least seven days on mexiletine they had no clear benefit. The four patients subsequently improved with carbamazepine or phenytoin. Our observations suggest that mexiletine alone is not of value in trigeminal neuralgia.