Preliminary studies indicate that activation of the immune system by risk factors for stroke (hypertension, hypercholesterolemia, diabetes and age) increases the risk of atherosclerosis and the formation of intravascular thrombosis. By measuring the levels of cytokine and leukocyte activation in the stroke prone population and age matched controls without risk factors, an attempt will be made to characterize those factors which potentially increase the risk for carotid atherosclerosis and subsequent cerebral infarctions.