Blood levels of superoxide dismutase (SOD), measured by radioimmunometric assay, were compared in 68 patients with chronic schizophrenia and 50 normal control subjects. Psychopathology in the patients was assessed with the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Positive Symptoms (SAPS), and the Scale for the Assessment of Negative Symptoms. Blood SOD levels were significantly elevated in schizophrenia compared with control values. SOD levels showed a positive relationship with the BRPS and the SAPS total score in patients.