Objective. A comparative evaluation of glutathione reductase (GR) and glutathione-S-transferase (GST) activities in erythrocytes and platelets of patients with schizophrenia. Material and methods. Fifty patients, 47 men and 3 women, aged 25—56 years (medium 34) with acute paranoid schizophrenia (F20.0 ICD-10) with hallucinatory-paranoid or paranoid syndrome were studied. The control group consisted of 48 healthy people, 45 men and 3 women, aged 21—59 years (medium 38). GR activity was determined by the oxidation of NADP-H in the reduction reaction of oxidized glutathione. GST activity was determined by the rate of chromogenic conjugate formation between glutathione and 1-chloro-2.4-dinitrobenzene. Results. No differences in the erythrocyte GR and GST activities between the control group and patients with schizophrenia were found. The platelet activity of GR and GST was significantly lower in patients compared to the control group (Mann—Whitney U test, p<0.01). Spearman rank correlation analysis showed that the erythrocyte GST activity was significantly correlated with PANSSneg scores when measured at the beginning of the study, GST was higher in those patients who had less PANSSneg scores after treatment (R=–0.41, p<0.05). The activity of platelet GST in patients with schizophrenia was correlated with the severity of positive symptoms (PANSSpos score) at the beginning of the study before taking therapy (R=–0.31, p<0.05), i.e. the more prominent psychotic symptoms were expressed in patients with lower GST activity. Upon completion of therapy, this association disappeared. Conclusion. The activity of glutathione-dependent enzymes in the blood cells of schizophrenic patients determined before the beginning of antipsychotic pharmacotherapy may be important for objective assessment of this metabolic system status and the degree of its impairment in patients.