Endothelial injury and platelet activation may be involved in the pathogenesis of hypertensive vascular disease. The aim of this study was to evaluate the change in endothelial cell and platelet activation plasma markers after an acute physiological increase in blood pressure. Plasma renin activity (PRA), serum angiotensin-converting enzyme (ACE), plasma factor VIIIR:Ag, and plasma beta-thromboglobulin (BTG) were determined before and after handgrip in subjects with borderline (n = 8) and established (n = 11) hypertension and in age-matched normal volunteers (n = 10). A significant mean increase in ACE, factor VIIIR:Ag, and BTG was observed after handgrip in all groups of subjects. A greater response in BTG changes was found in hypertensive subjects when compared with normal subjects. No correlations were found between the blood pressure response after handgrip and the handgrip-induced changes in plasma markers of endothelial cells and platelet activation. Changes in endothelial cells and platelet activity occurring after handgrip did not appear to depend on the associated blood pressure elevations.