The blood stream is affected by viscosity and many other haemorheological factors such as lipid peroxidation in the plasma and red blood cells. The aim of this study was to investigate the changes of haemorheological parameters after submaximal exercise in trained and untrained subjects. The results indicated that heart rate, lymphocyte count, erythrocyte deformability, plasma lipid peroxide levels and erythrocyte glutathione peroxidase activity are increased after submaximal exercise.