Potentially important new findings have recently been reported concerning the so-called metabolic syndrome in relation to the renin-angiotensin system, ie, that treatment with inhibitors of the angiotensin-converting enzyme (ACE) not only decreases blood pressure levels but prevents the development of diabetes mellitus. The new findings described in this article highlight the potential role of the ACE system in the regulation of insulin sensitivity, thus contributing to the development of type 2 diabetes and metabolic syndrome. In addition to the well known selective effects of ACE inhibitors and angiotensin II receptor blockers in reducing microalbuminuria in diabetic patients, the potential ability of these drugs to reduce the risk of diabetes and the metabolic syndrome would support their use as first line agents not only in diabetic patients but also in selected groups of hypertensive patients, who are particularly at risk of developing metabolic complications. This information supports the Joint Guidelines for the Management of Arterial Hypertension by the European Society of Hypertension and the European Society of Cardiology, which highlight the crucial role of ACE inhibitors and the angiotensin II receptor blockers in preventing the development of diabetes in hypertensive patients.