The pathological mechanisms of out-of-office hypertension (e.g., masked hypertension and workplace hypertension) have been remained unclear, but several mechanisms for this unique phenomenon have been proposed. Altered neurohumoral regulations, increased activity of sympathetic nerve and renin-angiotensin-system (RAS), and reduced baroreflex gain, coupled to a prolonged endothelial dysfunction, play an important role in out-of-office hypertension. Previous studies showed that angiotensin receptor blocker (ARB) reduced not only RAS but also sympathetic activity, and improved baroreflex as well asendothelial function, which suggested that ARB may be suitable for treating subjects with out-of-office hypertension. In the TROPHY (TRial Of Preventing HYpertension) study, it has been demonstrated that treatment with ARB reduced the risk of development of true hypertension from a pre-hypertensive state. Because there were close associations between pre-hypertension and out-of-office hypertension, especially in those with obesity and metabolic syndrome, this study may also provide an important information about the treatment strategy of out-of-office hypertension.