Recently, several lines of evidence have suggested the possible of immunological dysfunction in the pathogenesis of schizophrenia. We therefore investigated the ability to produce interferons and lymphokines in response to mitogenic or viral stimulation in a whole blood assay of 37 schizophrenic patients (DSM-III-R) and of 42 healthy blood donors. Phytohaemagglutinin (PHA) was used for the induction of interleukin-2 (IL-2), interferon gamma (INF gamma), interleukin-6 (IL-6) and the soluble interleukin-2 receptor (sIL-2R) and Newcastle Disease Virus (NDV) for the induction of interferon alpha 2 (INF alpha 2). All lymphokines and, in addition, the sIL-2R in the sera were determined by ELISA technique. The psychopathological status of the patients was assessed by psychiatrists according to internationally accepted standards. The patient group showed a trend to lower levels of the interferons alpha 2 and gamma and a significant decrease of IL-2 production. The sIL-2R levels were significantly increased in the sera of schizophrenic patients. The latter increase was associated with a poor assessment of prognosis (Strauss and Carpenter). This association appears to be of interest. However, its significance is not understood, since longitudinal studies could not be performed.