Previous observations have suggested the possibility of separating the borderline hypertensive population into two groups on the basis of blood pressure responses to maximal exercise testing. In order to evaluate the effects of 1 year of physical training on hypertensive subjects, 14 men with resting borderline hypertension and with a normal pressure response to exercise (group I) and 12 with resting borderline hypertension but with an abnormal pressure response to exercise (group II) underwent a maximal bicycle ergometer stress test in a sitting position before and after the training period. In group I, systolic and diastolic blood pressure levels both at rest and during submaximal exercise were significantly reduced after the training period. In group II, resting systolic blood pressure was unchanged, whereas resting diastolic pressure was significantly increased. During submaximal exercise, systolic and diastolic blood pressure showed only mild, nonsignificant differences when compared before and after training. No differences were found during maximal exercise. Blood pressure response to stress testing is useful to identify early stages of the disease and to plan preventive measures consisting of regular physical training either alone or associated with dietary and/or pharmacological treatment.