The hemodynamic and sympathoadrenergic responses during isometric handgrip and mental arithmetic tests were compared in 18 patients with mild essential hypertension. Mean blood pressure increased significantly after both maneuvers (27% during isometric stress and 10.7% during mental stress), but the increase was significantly higher during isometric stress (p < 0.001). Both Stressors increased the heart rate (p < 0.001) and cardiac output (p <0.001). However, the total peripheral resistance behaved differently, for R increased during isometric stress (p < 0.05) and remained unchanged during mental stress. Both Stressors increased the epinephrine levels (p < 0.005), but only isometric stress increased the norepinephrine levels (p < 0.001). It is concluded that both Stressors increase cardiac output by way of an increase in heart rate, but isometric stress also increases total peripheral resistance and thus causes a greater increase in arterial pressure. Isometric stress activates both the adrenergic and noradrenergic systems, thereby accounting for the exaggerated response in arterial pressure, whereas mental stress stimulates the adrenergic system only.