Aortoiliac arterial wall compliance was measured in apparently healthy subjects and in patients with non-insulin-dependent diabetes (NIDDM), on diet alone, who had no clinical evidence of peripheral arterial disease. Compliance was significantly lower in patients with diabetes. The two clinical groups were combined to provide as wide a range of blood glucose values as possible. After allowing for the influence of age, there were significant negative correlations between compliance and free fatty acid and insulin levels. These were almost completely accounted for by differences in blood glucose levels. Therefore, arterial compliance was best predicted on the basis of age and the area under the blood glucose curve.