A detailed history of a boy with Landau-Kleffner syndrome is presented, demonstrating a close relationship between language functioning and paroxysmal electroencephalogram activity. During a 3-year 6-month follow-up period, three abrupt deteriorations of all language functions occurred: the child became totally noninteractive with his environment within 1 week's time. Two of these deteriorations were reversed with steroid treatment, with an identical recovery phase. Intravenous immunoglobulins had a very dramatic and comparable effect in the third relapse; both language functions and electroencephalogram abnormalities were influenced significantly by the intravenous immunoglobulin treatment.