Two groups of patients were studied: 25 children with grand mal epilepsy who received anticonvulsive treatment with DFH (diphenylhydantoin) for 6 mo. and 25 children with infectious meningoencephalitis who required DFH to control convulsive crisis. Patients with a history of recurrent infections, lymphadenopathies, hepatosplenomegaly, drug allergy, collagenopathies and immunodeficiency, were ruled out from this study. In all patients T and B lymphocytes, serum IgA and saliva and duodenal fluid IgA determinations were made. There was an IgA concentration decrease in saliva and duodenal fluid of epileptic and meningoencephalitic patients (P < 0.05) and a T lymphocyte depression in epileptic and nonepileptic patients treated with DFH (P < 0.001).