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To investigate whether the clinic–daytime blood pressure difference can provide information on vascular reactivity to stress comparable to that of simple noninvasive stimuli such as a cold pressor test and isometric exercise, and whether there is any relationship between this blood pressure difference and noninvasive measurements of the left ventricular mass and carotid arterial wall.Patients with newly discovered, never-treated, sustained hypertension were included in the study after a 1 month run-in, during which time their blood pressure was measured three times at 2 week intervals.Blood pressure was measured by a noninvasive procedure at rest and during a cold pressor test and an isometric exercise. The difference was calculated for systolic, diastolic and mean blood pressure as resting minus daytime ambulatory blood pressure. Parameters of the posterior wall and septal thickness of the left ventricle, aortic root and left atrium were studied by M-mode echocardiography. Carotid wall thickness and diameter were measured using ultrasound.The 90 patients enrolled in the study were divided into tertiles of clinic–daytime blood pressure difference. The composition of the groups differed in sex, since the majority of women were in the highest tertile, but was comparable for age, body mass index, renin-aldosterone axis and lipid and carbohydrate metabolism. Blood pressure responses to cold and isometric exercise were more pronounced in patients in the lowest tertile of blood pressure difference. No intergroup differences were detected in echocardiographic parameters of ventricular (left ventricular mass, tertiles I–III: 46.5 ± 10, 42.3 ± 8,44.8 ± 13 g/m 2:7, respectively) and carotid (intima–media thickness, tertiles I–III 0.58 ± 0.1, 0.54 ± 0.1,0.62 ± 0.1 mm, respectively) structure.The present study indicates that the clinic–daytime blood pressure difference provides different information on cardiovascular reactivity compared with that obtained from the cold pressor test and isometric exercise. Moreover, it does not seem to have any relationship with ventricular hypertrophy and/or carotid wall thickening.