Introduction. Patients with essential hypertension react more strongly to mental stress than normotensives. This may be related to the type of stress coping or to increased reactivity associated with the disease. The aim of our study was to examine whether patients with essential or secondary hypertension differ in their reaction to mental stress. Methods. Seventeen patients with essential hypertension (EH), 9 patients with renal hypertension (RH), and 22 normotensive controls (N) with no circulatory disorders were subjected to a psychophysiological examination under mental stress. Blood pressure (BP), heart rate (HR) and electrodermal activity (EDA) were measured. Results. The two hypertensive groups differed in their BP reaction to mental stress from the control group but not from each other. The product of heart rate and systolic blood pressure during the matrix test was significantly higher in essential than renal hypertensives (EH median: 13344; RH median: 12154.5; p = 0.04). This also holds true for the number of spontaneous fluctuations of EDA in the resting phase after the experiment (EH. median: 3.2; RH. median: 1.3; p = 0.01). Conclusion. The results suggest that not only a high blood pressure level but also the sympathetic nervous tone are responsible for the blood pressure response to mental stress. Due to very different (perhaps psychosocially triggered) conditions, essential hypertension leads to a stronger cardiovascular reaction under mental stress than renal hypertension.