We have previously demonstrated that awareness of high blood pressure may increase blood pressure, plasma catecholamine levels, and stress responses. In the present study, three groups of 19-year-old men, all unaware of their blood pressure status, were selected from the first (group-1, 62±2 mm Hg, [mean±SEM], n=15), 50th (group-50, 90±4 mm Hg, n=15), and 99th (group-99,123±5 mm Hg, n=14) percentiles in casual mean blood pressure at a screening. They were studied (blinded examiners) with intra-arterial blood pressure recordings and multiple measurements of arterial plasma epinephrine and norepinephrine during a mental arithmetic challenge and cold pressor test Despite high mean blood pressure at the screening, group-99 did not differ from group-50 either in intra-arterial mean blood pressure after 30 minutes of supine rest (89±3 versus 86±2 mm Hg) or in serum lipids and resting plasma epinephrine and norepinephrine. However, in group-99 resting plasma epinephrine showed a positive hyperbolic relation to resting diastolic blood pressure (r=.73, P=.004) and a negative hyperbolic relation to the ratio of high-density lipoprotein cholesterol to total cholesterol (r=−.75, P=.002). None of these correlations were present in the two other groups. Furthermore, the three groups differed in heart rate responses (P<.0005) and systolic (P<.0005) and diastolic (P<.05) blood pressure responses to mental arithmetic challenge, group-99 being hyperreactive compared with the other two groups. Plasma epinephrine and norepinephrine responses to mental arithmetic challenge and blood pressure responses to the cold pressor test did not differ. However, changes in mean blood pressure showed a positive hyperbolic relation to plasma epinephrine during mental arithmetic challenge in group-99 (r=.81, P=.0004) but not in the two other groups. These findings support a link between high screening blood pressure, specific hyperreactivity to mental stress, and catecholamine-sensitive coronary risk factors.