A pilot study testing the hypothesis of a blood pressure lowering effect of polyunsaturated fatty acids was conducted in Evans County, Georgia. A moderate increase of dietary linoleic acid significantly decreased diastolic blood pressure in eight borderline hypertensives who were otherwise healthy, within four weeks. The change was not due to a reduced sodium content of the diet. A significant increase in creatinine excretion and clearance was noted, indicating an improvement in kidney function which might explain the blood pressure lowering effect of the fat-modified diet.