1 Cardiovascular and sympatho-adrenal responsiveness to mental stress (CWT; a colour word test), orthostatic testing (ORT) and a cold pressor test (CPT) were examined in three groups of hypertensive patients (n = 14-16) before and after 6 months treatment with metoprolol (243 +/- 26 mg daily), propranolol (149 +/- 16 mg daily) or hydrochlorothiazide (50 +/- 8 mg daily) in an open trial design. 2 Treatment reduced outpatient blood pressures in the three groups similarly (from approximately 155/102 to 135/90 mm Hg). During treatment resting blood pressures in the laboratory were clearly reduced by beta-adrenoceptor blockade but not by thiazide treatment. Metoprolol and propranolol caused similar reductions of basal heart rates and plasma glycerol levels, whereas only propranolol reduced cyclic AMP concentrations in plasma. 3 Before treatment CWT and CPT increased systolic and diastolic blood pressures by about 30%. Heart rate increased by about 30 beats min-1 during CWT and 10-15 beats min-1 during CPT and ORT. Small venous plasma adrenaline responses were evoked by all tests, whereas noradrenaline was elevated mainly by CPT and ORT. Dopamine levels did not change. 4 Heart rate responses to all stressors were markedly and similarly reduced, whereas blood pressure responses were essentially unchanged during metoprolol or propranolol treatment. In the thiazide group circulatory responses to CWT were slightly attenuated, whereas responses to ORT and CPT were unchanged. 5 The systolic blood pressure levels were reduced throughout the test session in all three groups, although less so in the hydrochlorothiazide group. Both beta-adrenoceptor antagonists clearly reduced diastolic blood pressure and heart rate levels at rest and during stress, whereas thiazide treatment caused no significant changes in these respects. 6 The rate pressure product, which increased by 80-100% in response to CWT before treatment, was more markedly reduced by beta-adrenoceptor blockade than by thiazide treatment both at rest and during stress. 7 Self ratings (visual analogue scales) of stress and irritation were increased by CWT in a similar fashion before and during treatment in all groups. beta-adrenoceptor blockade was associated with higher subjective ratings of tiredness at rest, but not after CWT. Performance in the CWT increased slightly more in the thiazide group. The physiological responses to CWT were not correlated to the subjective responses.(ABSTRACT TRUNCATED AT 400 WORDS)