Cardiac and skeletal muscle are very different functional tissues, and we would expect a variation in the ROS generation, in ageing and rigorous exercise-related in both tissues. We determined TBARS, total SOD, Cu, ZnSOD and MnSOD activities, and the patterns of SOD isoenzymes in skeletal muscle and heart of male Wistar rats, young and old, in rest and after rigorous exercise. There were no differences in the levels of lipoperoxidation in aged rest animals in both tissues, but the level was increased after exhaustion. The level of SOD activities was bigger in the heart than in skeletal muscle. Total SOD and Cu, ZnSOD activities were higher in old rest animals in the skeletal muscle than in young rest rats. This change did not occur in the heart. After rigorous exercise, the level of SOD activities was increased in young rats in both tissues. However, in old exhausted rats, the activities were only elevated in the heart. Different Cu, ZnSOD isoenzyme patterns showed in relation to tissues. In the skeletal muscle in old animals, the Cu, ZnSOD isoenzyme pattern was modified. The rigorous exercise did not change this pattern. The pattern of MnSOD isoenzyme was not varied in either tissue, age nor and exercise.