Ketosis is beneficial for seizure control, possibly through induction of cerebral acidosis. However, cerebral intracellular pH has not previously been measured in ketotic humans and the animal data are sparse. We describe a high-fat diet, avidly consumed by rats, that induced consistent and moderate ketosis. Adult male rats were fed either the high-fat ketogenic diet, a high-carbohydrate diet with the same protein content as the ketogenic diet, or regular laboratory chow. Five to 6 weeks later, the rats were anesthetized, paralyzed, and injected with neutral red; their brains were frozen in situ. Intracellular pH of the cerebral cortex and cerebral glucose, lactate, ATP, phosphocreatine, and gama-aminobutyric acid (GABA) levels were measured. Rats fed the ketogenic diet had > 10-fold increase in their plasma ketones, but we noted no significant differences in cerebral pH or in cerebral metabolites and GABA levels among the three groups. Therefore, the antiepileptic effect of the ketogenic diet probably is not mediated by cerebral acidosis or changes in total cerebral GABA levels.