Phenobarbital is still the most effective anticonvulsant in treatment of grand mal epilepsy. Phenobarbital, if incompletely effective, when used alone, is still more effective when supplemented with either Dilantin or Mesantoin than any single drug used alone or in other combination. Using a supplemental drug when indicated doubles the number of patients that respond to phenobarbital. Maintaining a reasonable dosage results, in this study, in complete absence of toxic effects from phenobarbital. Mesantoin is twice as effective as Dilantin as an anticonvulsant but is twice as toxic.