Reproducibility of noninvasive ultrasound methods for vascular diagnosis was studied in 36 patients with Insulin Dependent Diabetes Mellitus. The vascular examination included a) the measurement of ankle systolic arterial pressure and ankle/arm pressure index (c.w. Doppler), b) Echo-Doppler examination of iliac arteries with measurement of maximum systolic frequency, systolic spectrum width and diastolic reverse flow component. A grading of iliac artery stenosis was also performed. The examination was repeated after one month according to a blind protocol. The coefficients of variation were as follows: 8% for ankle pressure; 8% for ankle/arm pressure index; 9% for the maximum systolic frequency; 18% for the spectrum width and 15% for the reverse flow component. The reproducibility of the grading of iliac artery stenosis based on the combined use of the three Echo-Doppler parametres was measured by the Kendall coefficient (W = 0.865). These results confirm that non invasive methods are suitable and reliable for investigating vascular disease in diabetic patients. Accurate estimates of reproducibility are essential pre-requisites for the planning of studies on the natural history of vascular disease and on progression-regression of arterial lesions.