In a study aimed at comparing the effects of beta-blockers and thiazide diuretics on responses to stressful provocations, 45 essential hypertensives (WHO I-II) were treated with either the selective beta-blocker metoprolol (METO), the non-selective beta-blocker propranolol (PROP) or hydrochlorothiazide (HTZ) for 6 months. Blood pressure, heart rate and plasma catecholamines were measured in connection with a mental stress test and a cold pressor test before and during therapy. All drugs reduced outpatient blood pressure similarly, but beta-blockade reduced blood pressure and heart rate levels more efficiently at rest and during stress in the laboratory. Heart rate reactivity to stress was reduced mostly by beta-blockade during mental stress. Blood pressure and sympatho-adrenal reactivity were unchanged by therapy. Stress reactivity failed to predict antihypertensive responses. The results suggest that beta-blockade may be more effective than diuretic treatment in reducing blood pressure levels and cardiac workload as assessed by the rate pressure product in stressful situations.