Two groups of adult-onset diabetics, matched according to 10 different criteria, were followed, biochemically and fluorescein-angiographically, over a period of 6 years. One group used a saturated-fat diet, and the other group of patients were on an unsaturated-fat diet, particularly rich in linoleic acid. Statistically significant differences were found in biochemical data and in the progression of diabetic microangiopathy between the two groups. The conclusion is warranted that a linoleic acid-rich diet, administered over an extended period of time, may inhibit the development of microangiopathy, or the deterioration of diabetic retinopathy.