The network consists of five field centers, a central biochemistry laboratory, a molecular genetics laboratory, and a data coordinating center to study an equal sample of Black and non-Black families with two or more hypertensive siblings, untreated relatives, and controls for genetic association and sib-sib linkage studies. The studies, using samples from the Family Heart Study (FHS) and the Atherosclerosis Risk in Communities (ARIC) study, include determination and characterization of genes promoting hypertension and interaction with non-genetic factors.