Excess body weight correlates closely with increased blood pressure. Virtually every prospective study of factors that influence blood pressure regulation has identified weight, or body mass index, as the strongest predictor of human blood pressure. In normotensive persons, longitudinal and intervention studies have documented that weight gain, over as short a period as 1-2 mo., is associated with predictable rises in arterial pressure. Conversely, in borderline hypertensive persons, similar types of studies have reported that weight reductions of as little as 4-5 kg result in normalization of blood pressure. During periods of weight loss, decreases in blood pressure are evident within the first 2-3 wk; the greatest proportionate blood pressure change occurs during the earliest phases of weight reduction. The decline in blood pressure with weight loss has been shown to be unrelated to variations in nutrient intake. However, the association between blood pressure decreases and increased amounts of physical activity, which generally accompany weight loss efforts, is less clear. For many overweight individuals, reductions in blood pressure that occur with weight loss may be due specifically to the initiation of a regular physical exercise regimen. Weight loss in hypertensive persons has been shown to dramatically reduce, and in many cases eliminate, antihypertensive medication requirements. It is estimated that in up to 50% of the adults in the United States whose hypertension is being pharmacologically managed, the need for drug therapy could be alleviated with only modest reductions in body weight.