Production of interferon (IFN)-alpha and -gamma by leukocytes from 34 patients with acute schizophrenia and 34 controls was measured before and after 5-6 weeks of antipsychotic treatment by using Sendai virus as IFN-alpha inducer and lentil lectin as inducer for IFN-gamma production. The schizophrenia series included 13 first admission patients (mean duration of illness 1.1 years) and 21 re-entry patients (mean duration of illness 10.1 years). Of the total series 23 were drug-free at the time of pretreatment sampling. In all subgroups the schizophrenic patients produced less IFNs than healthy controls although the differences reached statistical significance only in the total group of schizophrenic patients with regard to production of IFN-alpha. The antipsychotic drug treatment did not have an effect on IFN production. The techniques used, the influence of genetic factors, and eventual clinical implications are discussed.