We investigated the magnitude of the pressor response to the clinic with ambulatory monitors by comparing blood pressure readings related to the medical visit with all clinic-unrelated readings during the day. One hundred studies were conducted on 51 hypertensive patients who were placed either on placebo (67) or on monotherapy with hydrochlorothiazide, atenolol, or the converting enzyme inhibitors captopril or zofenopril. On placebo, clinic-related systolic (162 +/- 2), diastolic (101 +/- 1), and pulse (61 +/- 2) pressures (mm Hg) were significantly higher than the respective clinic-unrelated values (149 +/- 2, 93 +/- 1, and 56 +/- 1 mm Hg). Heart rates were not different. Despite significant reductions of blood pressure, the same pattern was found during treatment. After initiating the monitoring and while in transit to job or home (initial component of the clinic-related readings), systolic (166 +/- 2 mm Hg) and pulse (64 +/- 2 mm Hg) pressures were higher than those during return to the office the next day (final component, 158 +/- 3 and 58 +/- 2 mm Hg). Blood pressures of both components, however, were significantly higher than the clinic-unrelated ones. In 19 repeat studies carried out 2-24 months apart on placebo, the average pressor response did not change from the first (13 +/- 3/11 +/- 2) to the second (13 +/- 4/11 +/- 2 mm Hg) procedure. No correlation, however, was found between the first and second study responses of individual patients.(ABSTRACT TRUNCATED AT 250 WORDS)