Hypertension is a polygenic and multifactorial disease and is intimately related to salt homeostasis. Four important vasoactive peptide systems participate in regulating blood pressure and salt homeostasis. Their interplay is indispensible in many physiologic and pathologic conditions. While the renin-angiotensin and the endothelin systems raise blood pressure by inducing vasoconstriction and sodium retention (or excretion), the kallikrein-kinin and the natriuretic peptide systems reduce blood pressure by eliciting vasodilatation and natriuresis. Gene targeting as well as transgenesis have provided us a lot of information on the biological functions of the genes of these systems. Animal models from these technologies are discussed in relation to blood pressure regulation.