Plasma levels of interleukin (IL)-1 beta and IL-6 were measured in 60 acutely hospitalized psychiatric patients and in 60 healthy controls by enzyme-linked immunosorbent assay (ELISA). Almost no IL-6 was detected in the plasma of the patients or controls. The mean level of IL-1 beta was found to be significantly higher in schizophrenic patients than in their corresponding controls (P = 0.03). The acute schizophrenics, but not the group of chronic schizophrenics, contributed to this increase. No correlation with age, duration of illness or overt psychopathology was found. The neuroleptic medication did not prove to have a significant effect on the plasma IL-1 beta levels. There was no difference between non-psychotic affective disorder patients (N = 17) and the controls.