"White coat" hypertension can be demonstrated in 20-25% of younger patients with mild-to-moderate hypertension. In a population of 50 untreated hypertensive patients > or = 70 years (mean age 79 +/- 6 years, office blood pressure > or = 160 mmHg systolic and > or = 95 mmHg diastolic) ambulatory blood pressure monitoring, ECG and echocardiography were performed to assess the frequency of "white coat" hypertension and the alerting reaction ("white coat" effect). "White coat" hypertension was diagnosed, if mean daytime ambulatory blood pressure was < or = 146/87 mmHg (taken as upper "normal" limit), "definite" hypertension, if > 146/87 mmHg. Nine patients (18%) were classified as "white coat", 28(56%) as "definite" hypertensives, 13(26%) as an "intermediate" group. There were no differences in gender, weight, concomitant diseases, pre-study treatment, and systolic or diastolic left ventricular function between the groups. Patients with "white coat" hypertension showed lower office blood pressure (178 +/- 13/98 +/- 3 vs 201 +/- 19/104 +/- 7 mmHg; p < 0.004), lower left ventricular mass index (131 +/- 9 vs 139 +/- 26 g/m2, p < 0.5), no left ventricular hypertrophy (ECG-criteria; p < 0.05), a more pronounced alerting reaction (39 +/- 13/22 +/- 5 vs 27 +/- 17/8 +/- 9; p < 0.01) and no correlation between office blood pressure and left ventricular mass compared to the "definite" hypertension group. The total group showed an average alerting reaction of 30 +/- 19/12 +/- 8 mmHg. It is concluded that "white coat" hypertension and an alerting reaction can be demonstrated in untreated elderly and very elderly hypertensive patients. Patients with "white coat" hypertension are characterized by a milder degree of hypertension, less cardiac target organ damage and a more pronounced alerting reaction. The prognostic significance of "white coat" hypertension in the elderly needs to be reevaluated in a larger population.