Indirect automatic 24-hour blood pressure monitoring has been found to be reliable and valid and thus has been introduced for the evaluation of dosage and efficacy of antihypertensive drugs. The present double-blind placebo-controlled randomized long-term study reports the therapeutic results of the oral administration of a new beta-adrenergic blocking agent, carvedilol, with direct vasodilator activity in patients with primary hypertension. The antihypertensive effect was acute at onset and comparable in the supine and standing position judged by casual blood pressure readings. Indirect automatic blood pressure monitoring demonstrated a good antihypertensive effect throughout daily activities after single oral dosage. Despite some technical problems with the apparatus (Pressurometer III, Del Mar Avionics), a circadian pattern could be documented in both untreated and treated patients. Blood pressure and heart rate were normally distributed but less variable during treatment. The long-lasting antihypertensive effect was comparable to the commonly used beta-blocker metoprolol. A significantly reduced awakening blood pressure in the morning may indicate a beneficial effect on a possible prognostic factor in arterial hypertension.