It has been demonstrated that the activity of nitric oxide synthase (NOS), cyclooxygenase (COX), xanthine dehydrogenase/xanthine oxidase, myeloperoxidase, myeloperoxidase (MPO), and other enzymes promoting ROS production increase following stroke, whereas the activity of enzymes that prevent ROS production, such as superoxide dismutase (SOD), catalase, peroxidase, glutathione peroxidase (GSH-Px) decrease, consequently destroying the dynamic balance of ROS, and leading to its accumulation. This evidence concerns the gene XDH and Stroke.