The aim of this study was to evaluate the concentration of malondialdehyde-MDA (one of the lipid peroxidation products)-in blood plasma and erythrocytes and the activity of superoxide dismutase (SOD) and catalase (CAT) in red blood cells of patients with a primary brain tumour. The study was performed on 24 patients with a brain tumour (9 with glioblastoma and 15 with asrocytoma) treated in the Department and Clinic of Neurosurgery and Neurotraumatology at Ludwik Rydygier Medical University in Bydgoszcz. The control group consisted of 20 healthy volunteers. A statistically significant higher MDA concentration in erythrocytes and blood plasma and a higher activity of SOD or CAT in erythrocytes was shown in patients with a brain tumour as compared to the control group. Neither the histological type of tumour nor surgery has an effect on the tested biochemical parameters.