Quantitative evaluation of brachial artery diameter, blood velocity and flow (pulsed Doppler velocimetry) and of forearm arterial compliance (FAC) - mathematical analysis of the simultaneous diastolic pressure and flow according to a first-order arterial model - was carried out in 10 normotensive controls, and in 23 borderline hypertensive patients, of the same age. Using a value of 2 standard deviations above the average cardiac index of 20 normotensive subjects, enabled us to classify 12 patients as having a normal cardiac output and 11 patients as having a high cardiac output. Each group was of similar age and pressure. FAC was lower in patients with a normal cardiac output than in normal controls (P<0.01) and also lower than in patients with high output (P<0.01). Brachial artery diameter and flow were higher in patients with high output than in normal controls (P<0.01,P<0.001) and also higher than in patients with a normal output (P<0.001). A positive correlation (r=0.55;P<0.01) was found between heart rate and brachial artery diameter in the 23 patients. These results demonstrate a non-homogenous pattern of brachial artery characteristics of patients with borderline hypertension. Patients with normal cardiac output exhibited a clear reduction of the distensibility of the forearm arteries while patients with high cardiac output had strong dilation, of the brachial artery.