Comparison of the antihypertensive efficiency of nitrendipine, metoprolol, mepindolol and enalapril using ambulatory 24-hour blood pressure monitoring. In a randomized 6-month study of 201 patients, the antihypertensive efficiency of the calcium antagonist nitrendipine, the beta 1-selective blocker metoprolol, mepindolol, the beta blocker with intrinsic activity and the angiotensin-converting enzyme inhibitor enalapril were compared as monitored by 24-hour ambulatory blood pressure (BP) measurements. The study was designed so that a comparable decrease in casual BP values was obtained with all 4 drugs. If normotension was not achieved with monotherapy, a diuretic also was administered. Pretreatment casual BP and mean 24-hour ambulatory BP values did not differ between the 4 groups. Normotension as assessed by casual BP measurements was observed in all 4 groups after 6 months of therapy, there being no significant differences between the groups. However, significantly more diuretics were required in the mepindolol (n = 14) and in the enalapril (n = 20) groups compared to the nitrendipine (n = 5) and metoprolol (n = 7) groups. Despite comparable casual BP control, the 4 groups differed significantly in their mean 24-hour measurements. The greatest systolic and diastolic BP decreases were seen in the metoprolol group. Metoprolol was also the most effective drug in decreasing the frequency of systolic pressure peaks greater than 180 mm Hg. Both beta blockers and enalapril significantly decreased the morning BP increase compared to the values before treatment, while nitrendipine did not. These data show that casual BP measurement is not a good predictor of 24-hour BP in patients taking hypertensive therapy. Despite an equal degree of "office" BP control, different antihypertensive regimens do not confer the same degree of "nonoffice" BP control. 