High blood pressure is one of the most common health problems in this country. It can be caused by many factors, including stress, diet, diabetes, kidney disease, or obesity. In many people, there is no identifiable cause for their high blood pressure. If high blood pressure goes untreated, it can lead to heart failure, kidney failure, or stroke. Previous studies have shown that variations in three genes in chromosome 1—ATP1B1, RGS5, and SELE—cause some people to be more susceptible to developing high blood pressure. All three of these genes are involved in the development of proteins that play a role in regulating blood pressure, but it is not known exactly how variations in these genes affect blood pressure levels. This study will examine previously collected genetic samples from participants in two clinical trials, the GenNet study and the Heredity and Phenotype Interaction (HAPI) Heart study. Study researchers will analyze the samples to identify and characterize variations in the ATP1B1, RGS5, and SELE genes. Results from this study may lead to more effective diagnostic and treatment options for people with high blood pressure.