This article focuses on the links between insulin and blood pressure at the level of the renin-angiotensin-aldosterone system (RAAS). The effects of insulin on plasma potassium levels and whole-body potassium content and the effect of potassium on glucose-induced insulin release identify a physiological glucose-potassium cycle. The normal interactions of insulin and hyperglycemia with the hormones of the RAAS are reviewed, and their changes in patients with diabetes mellitus are discussed. Some key findings on the interrelationships of insulin and the RAAS with regard to sodium metabolism are also brought into focus. A role for changes in the RAAS secondary to insulin resistance, hyperinsulinemia, and hyperglycemia is delineated in relation to the excess hypertension of diabetes. The effects of angiotensin-converting enzyme inhibition on insulin sensitivity and glucose tolerance are reviewed in the context of the glucose-potassium cycle.