The kindling of amygldaloid and cortical seizures in cats was used to study the prophylactic effects of phenobarbital, phenytoin, ethosuximide, acetazolamide, and dexamethason. Phenobarbital prevented the evolution of such seizures beyond stage 4 in all amygdaloid-kindling animals during 160 days of study. The prophylactic effect persisted on periodic challenge after the drug had been discontinued. Phenytoin, ethosuximide, acetazolamide, and dexamethasone appeared to have no prophylactic effect against the development of kindled amygdaloid seizures. With cortical kindling, both phenobarbital and phenytoin retarded the evolution of seizures without achieving true prophylaxis. The drugs appeared to act as suppressants. Prophylaxis was not an "all-or-none" phenomenon but rather a limitation of the stage of seizure evolution.