Dr. Hopkins and his collaborators are addressing the hypothesis that mutations at selected genes contribute to the development of essential hypertension. The method employed in this study to test the hypothesis is the ""affected sibling pair method"". The phenotypes studied include modulation status, salt sensitivity, renin stasis, kallikrein excretion, and red cell ion flux. This is a collaborative effort being carried out at three sites, Salt Lake City, Boston, and Paris. Approximately 100 sibling pairs with early-onset hypertension are to be studied at each site.