Thromboembolic complications such as ischemic stroke and myocardial infarction are significantly more frequent in patients with arterial hypertension. From the available intervention studies, it appears that pharmacologic treatment of hypertension-at least with diuretics and beta-blockers-may more effectively protect against cerebrovascular as compared to coronary thromboembolic events. Whether other antihypertensive substances provide a more effective protection with respect to cardiac morbidity and mortality is the subject of numerous studies presently underway. These studies will help to answer the question of whether the extent of protection from coronary events during antihypertensive treatment depends on factors beyond blood pressure control. The fibrinolytic system is crucially involved in the pathogenesis of thromboembolic events. One determinant of this system is the balance between plasminogen activators (tissue-type plasminogen activator [t-PA]) and inhibitors (plasminogen activator inhibitor 1 [PAI-1]). Experimental and clinical evidence suggests that at least some of the drugs used in the treatment of hypertension may alter the activity of the fibrinolytic system. Scarce and controversial data with respect to such an interaction exist with respect to diuretics, beta-blockers, and calcium antagonists. In addition, experimental evidence demonstrates that PAI-1 is stimulated by angiotensin II (A II), whereas t-PA is activated by bradykinin. Thus, antihypertensive drugs acting within the renin angiotensin system should exert effects also within the fibrinolytic system. However, results from clinical studies with angiotensin converting enzyme (ACE) inhibitors and A II receptor antagonists do not unequivocally support such a concept. The discrepancy in the results may, at least in part, be explained by studies performed in healthy volunteer subjects showing that ACE inhibition profoundly affected fibrinolysis only during stimulation of the renin angiotensin system by NaCL restriction.