At least 50 million adult Americans have hypertension, one of the most important modifiable risk factors for coronary heart disease, stroke, and end-stage renal disease. Dietary nutrient intake has been related to the etiology of hypertension, and nutritional intervention has become an important approach for the treatment and prevention of hypertension. While the effect of dietary intake of sodium, potassium, and alcohol on blood pressure (BP) has been studied intensively, the effect of dietary macronutrients, such as protein, has not been as well studied. The overall objective of this study is to examine the effect of dietary protein supplementation on BP. We propose to conduct a randomized, double-blind, placebo controlled 2-center trial in 280 healthy participants with BP higher than optimal level or stage-1 hypertension (systolic BF 120-159mm Hg and diastolic BP 80-95 mm Hg without clinical cardiovascular disease, chronic renal disease or diabetes). The trial will utilize a 3-phase cross-over design and have greater than 90 percent power to detect a 2.0 mm Hg reduction in systolic BP and a 1.5 mm Hg reduction in diastolic BP. The study participants will be recruited by mass mailing and work-site/community-based BP screening in New Orleans, Louisiana, and Jackson, Mississippi. Following a 2-week run-in period, eligible participants will receive 40-gram soy protein, 40-gram milk protein, and 40-gram complex carbohydrates (control) per day for 8 weeks in a random order. A 3-week washout period will be applied between intervention/control phases. The primary outcome will be difference in systolic and diastolic BP between soy protein supplementation, milk protein supplementation, and placebo control phases. In addition, differences in fasting plasma insulin, glucose, leptin, and homocysteine, serum lipids, waist and hip circumferences will be tested, and the impact of these variables on the mechanism of any BP-lowering effect will be examined. Results from the proposed study may provide the scientific evidence for protein supplementation recommendations for the prevention and treatment of hypertension in the general population.