Peripheral Atherosclerosis (PA) is a frequent complication of longstanding diabetes. Nevertheless uncertainty exists on defining risk factors (RF) for PA in diabetics. In order to elucidate this matter, at an early stage of the vascular complication, 54 non insulin dependent diabetic (NIDDM) patients, males, age range 40-59 years, without clinical signs of PA, were investigated by digital pulse plethysmography, measuring the inclination time (IT) of the pulse wave. A significant correlation was found between systolic blood pressure (BP) or fasting serum cholesterol (FSC) and IT (r = .28 p less than .05 and r = .34 p less than .05). IT was significantly higher in insulin treated patients compared with those on oral hypoglycemic treatment (154 +/- 41 msec; 122 +/- 25 msec; p less than .05) (M +/- SD). No significant effect on IT was induced by body weight, diastolic BP, serum triglycerides. A positive correlation was found between the number of RF (FSC greater than or equal to 220 mg/dl; systolic BP greater than or equal to 160 mmHg; insulin treatment) in each patient and IT (r = .55 p less than .001). In the absence of RF, IT was similar to that in non diabetic, normocholesterolemic, normotensive men of the same age (119 +/- 27; 116 +/- 15). FSC, systolic BP and insulin treatment are major RF for PA in male NIDDM patients. The condition is worsened by the simultaneous presence of two or more RF together.