Blood pressure fluctuates during daytime hours in response to changes in activities and to daily life stressors. Lifestyle factors may influence changes in blood pressure through a modulation of the sympathetic nervous system s activity, which is often elevated in subjects with borderline hypertension. In the HARVEST smoking, consumption of coffee, intake of alcohol, physical activity habits, and use of oral contraceptives influenced daytime blood pressure to a greater extent than did office blood pressure and had an effect on sympathetic tone (determined by measuring levels of urinary catecholamines). Subjects with borderline hypertension have a greater than normal risk of cardiovascular morbidity and mortality, but few data on the relation between ambulatory blood pressure and hypertensive complications during the early stage of hypertension are available. In the HARVEST the impact of ambulatory blood pressure on the walls of the left ventricle and on left ventricular mass in women was remarkable, whereas it was weak for men. The assessment of left ventricular systolic function confirmed that ejective performance in many young borderline hypertensive subjects is greater than normal. However, in 9.2% of the HARVEST participants left ventricular contractility evaluated by midwall measurement was found to be depressed. Although the prevalence of microalbuminuria (rate of excretion of urinary albumin > or = 30mg/24h) appeared to be low (6.1%), rate of excretion of albumin was highly statistically significantly correlated to 24h blood pressure. Ambulatory blood pressure monitoring is useful for identifying those borderline hypertensive subjects for whom antihypertensive treatment should be started.