The aim of the work was to study certain parameters of aerobic metabolism in the erythrocytes of multiple sclerosis patients and healthy controls after exposure of the erythrocytes to ionising radiation. The group of patients included 32 cases (17 women and 15 men) aged 19-54 years. The control group comprised 60 healthy subjects (28 women and 32 men) aged 19-56 years. The erythrocytes were exposed at +20 degrees C in contact with air during 50 minutes. The source of gamma radiation was 60 Co of 1.33 MeV energy and 10 Gy/min yield. In the erythrocytes of the patients the activity of the antioxidative enzymatic system was reduced, with decreased activity of superoxide dismutase (SOD-1) and glutathione peroxidase (GPx) and with increased level of malonyl dialdehyde (MDA) at the same time gamma radiation as an additional source of free radical generation increased the changes of these biochemical parameters which suggested a greater susceptibility of multiple sclerosis erythrocytes to oxidative stress.