This proposal is for Phase I, or, the "Treatment of Mild Hypertension Study" (TOMHS). Men and women with mild hypertension (DBP 90-99 mmHg) not on drugs, and DBP less than 95 mmHg on drugs, who are 45-69 years of age and free of evidence of end-organ damage related to their hypertension, will be recruited and randomized intothe "Phase I" study. Randomization will be carried ut to one of four possible treatment conditions: 1) placebo 2) chlorthalidone 3) atenolol 4) prazosin. The study is a double-blind controlled trial. All groups will be simultaneously given advice on non-pharmacologic methods designed to lower blood pressure including weigh control, dietary sodium reduction, and reduction of alcohol intake. The non-pharmacologic intervention will be initiated at the second eligibility visit (of three). Clinic visits will be conducted at a minimum of every three months and annually on all participants. Standard measures will be made at baseline and at subsequent clinic visits and at visits of record of blood pressure (random-zero), weight, overnight urine for sodium, potassium and creatinine, blood chemistries, ECG, Holter monitors, and echocardiograms. Four clinical centers will recruit 125 participants each. The study will be coordinated and administered centrally by the University of Minnesota, School of Public Health, Divisions of Epidemiology and Biometry. The major endpoint in Phase I is blood pressure change from baseline and for Phase II is hypertension related mortality and morbidity, including evidence of end-organ damage. The Phase I feasibility study inclues six months of planning, two months of training twelve months of recruitment, and average follow-up of approximately twenty months, six months of analysis and renewal preparation, and nine months for transition to Phase II of the study.