Arterial hypertension (HTN) increases the risk of cerebral coronary, and other vascular complications that frequently involve platelet activation and blood coagulation. Several key proteins in the blood coagulation, fibrinolytic and inhibitory systems were studied in 29 men with HTN (aged 45 +/- 3 yr) and 15 normal men of the same age. Plasma levels of high-molecular-weight kininogen and factors XII, IX, VII, X, II, and XIII, as well as von Willebrand factor (vWF), fibrinogen, fibronectin, alpha 2-antiplasmin, tissue-plasminogen activator, D-dimer, platelet factor-4, and protein C were measured by the use of appropriate functional and immunologic assays before and after a cardiopulmonary exercise stress test. The concentrations of vWF, alpha 2-antiplasmin, and D-dimer were significantly (P < 0.02) higher in the HTN group as compared with the control group. The exercise stress test resulted in significant rises in the plasma vWF, alpha 2-antiplasmin, and tissue-plasminogen activator levels in the two groups. The concentrations of vWF and D-dimer were related to diastolic blood pressure (r = 0.44 and 0.40, respectively; P < 0.02). Levels of vWF also were related to left ventricular mass index and left ventricular posterior wall and septal thickness (r = 0.34, 0.43, and 0.34, respectively; P < 0.05). The constellation of these findings suggests a low-grade fibrin formation and degradation, the magnitude of which is related to the diastolic blood pressure. The observed abnormalities can potentially contribute to the cardiovascular complications of untreated HTN.