The authors have effectively treated a case of true trigeminal neuralgia involving the 3rd branch of the 5th cranial nerve by mandibular nerve block with alcohol and Dilantin administration, and reached following results. 1. Alcohol injection has a definite value as the primary treatment of trigeminal neuralgia. 2. It is not yet to be clarified whether the effects of alcohol injection and Dilantin therapy reveal synergism. 3. Phenobarital was given as an adjuvant of Dilantin, but its effect on the painful paroxysms is questionable.