Systolic and diastolic blood pressure, heart rate, and circulating levels of catecholamines and cyclic AMP were measured during the handgrip test in 18 borderline hypertensive patients, 22 stable hypertensive patients, and 20 normotensive control subjects. No difference was observed, at rest, for plasma levels of noradrenaline, adrenaline, dopamine, and cyclic AMP among the three groups. During the handgrip test in borderline hypertensive patients, the percentage of increase of plasma levels of noradrenaline, adrenaline, dopamine, and cyclic AMP were significantly more elevated with respect to the levels of control subjects but not when compared with those of stable hypertensive patients. These results are in agreement with the hypothesis that in both borderline and stable hypertension there is an exaggerated sympathetic response to the handgrip test.