To evaluate the prevalence of 'white-coat' hypertension in patients with newly diagnosed hypertension, 255 subjects (131 males and 124 females) underwent 24-h ambulatory blood pressure monitoring. Patients with 24-h systolic and diastolic blood pressure < 135/85 mmHg were classified as white-coat hypertensives and the remaining as sustained hypertensives. On the assumption that white-coat hypertensives may not need to take antihypertensive medication, we evaluated the impact on cost of health care of two strategies based essentially on treating all patients according to casual blood pressure, or ambulatory blood pressure monitoring, followed by drug treatment in sustained hypertensives only. Of the 255 hypertensives studied, 54 (21%), confidence interval 16%, 26%, were classified as white-coat hypertensives. The age, sex-ratio and body mass index did not differ between the white-coat and the sustained hypertensive subjects. The strategy of monitoring all patients and of treating only the sustained hypertensives resulted in a substantial coat saving, which was calculated to be about 110,000 U.S.A. dollars over a period of 6 years. In conclusion, white-coat hypertensives are frequent among patients with newly diagnosed hypertension, and they do not differ from sustained hypertensives as regards demographic data. Ambulatory blood pressure monitoring, when used to decide whether or not to treat pharmacologically, increases the cost-effectiveness of treatment for hypertension and reduces the cost of health care.