Generalized infections or encephalitis due to herpesvirus are being recognized with increasing frequency. Recognition of these infections is facilitated by a high index of suspicion, by careful history of contacts with herpesvirus infection during the perinatal period, and by familiarity with clinical syndromes compataible with such infections. Diagnosis is confirmed by isolation of virus from blood or tissues; however, isolation of herpesvirus from other specimens may be helpful. The prognosis in patients with generalized herpesvirus infections or encephalitis is so dismal that early confirmation of diagnosis is indicated. Biopsy specimens should be studied by direct viral isolation procedures, fluorescent antibody techniques, and microscopic examination for characteristic intranuclear inclusions. Therapeutic trials with idoxuridine (IDU) and supportive measures deserve further study.