The objective of this study was to compare the effects on blood pressure of predominantly insoluble fiber (whole wheat and brown rice) and soluble fiber (barley) in a whole-grain diet. Subjects (seven men, nine premenopausal women, and nine postmenopausal women) consumed a controlled Step I diet for 2 weeks; then about 20% of energy was replaced with whole wheat/brown rice, barley, or half wheat-rice/half barley, for 5 weeks each. Blood pressure was determined weekly and weight daily before breakfast. Urinary excretions of minerals that might affect blood pressure and urea nitrogen were determined each period. Systolic pressure was lower after the wheat/rice and half-and-half diets. Diastolic and mean arterial pressures were reduced by all whole-grain diets. No differences were observed in urinary measurements. In a healthful diet, increasing whole-grain foods, whether high in soluble or insoluble fiber, can reduce blood pressure and may help to control weight.