Some patients currently receiving therapy for uncomplicated, mild to moderate essential hypertension may have been started on medication because of transient increases in office blood pressure (BP) or because of "white coat hypertension." As a consequence, many patients who do not have persistent hypertension may be receiving therapy for this diagnosis. This possibility was examined by discontinuing medication in 98 patients without target organ damage who were receiving longterm antihypertensive therapy under the care of their family physician in the community. Development of hypertension was based upon an increase in the patient's ambulatory BP (mm Hg) to > or = 160/95 recorded during usual daily activities. Evidence of early target organ damage was sought by using echocardiography to measure changes in left ventricular mass during the period off therapy. In the 50 patients who remained off treatment for 1 year, mean ambulatory BP increased (P < .001 from baseline (128 +/- 2/76 +/- 1) to 139 +/- 1/82 +/- 1 at 1 year, but remained lower (P < .001) than corresponding office readings performed by the patient's family physician (baseline: 138 +/- 2/83 +/- 1; 1 year: 150 +/- 2/89 +/- 1). At 1 year, ambulatory BP was < 150/90 and < 140/90 in 41 and 21 patients, respectively. Withdrawal of therapy did not produce any changes in left ventricular mass index (g/m2) with the mean value at 1 year (104 +/-3) being similar to baseline (103 +/- 3). Of the remaining patients, 35 redeveloped hypertension and 13 restarted therapy for reasons unrelated to BP. Many patients with treated, uncomplicated, mild to moderate hypertension may tolerate withdrawal of antihypertensive drug therapy without developing persistent hypertension or any increase in left ventricular mass.