The purpose of the study was determination of the activity of superoxide dismutase (SOD-1) in the erythrocytes of multiple sclerosis patients taking into consideration certain aspects of the disease, such as its duration, clinical form and course, age and sex of the patients. The study included 34 patients (17 males and 17 females) aged 19 to 56 years. The control group comprised 64 healthy subjects (25 females and 38 males) aged 19-59 years. A significant reduction was found of SOD-1 activity in the erythrocytes of the patients which may suggest a lower enzymatic defense mechanisms against oxidative stress. No difference in the activity of SOD-1 was found between clinical forms and different courses of the disease, although the activity changed in relation to age, sex and disease duration.