The effects of the prostaglandin I2 derivative beraprost sodium (Dorner) on ankle pressure index (AP; ankle joint-to-upper extremity systolic pressure ratio), subjective symptoms, and intermittent claudication were investigated in diabetic patients with arteriosclerosis obliterans (ASO). Forty patients (25 men and 15 women), mean age 63.9 years, were enrolled in this study. ASO was grade I in 30 patients, grade II in seven, grade III in one, and grade IV in two according to the Fontaine classification. They were administered six tablets (20 microg/tablet) of beraprost sodium daily for 6 months. At 3 and 6 months, API had significantly increased and symptoms such as coldness, numbness, and lack of feeling in the lower extremities were significantly improved. Ten evaluable patients increased ambulatory distance by approximately threefold, suggesting an improvement in intermittent claudication. Adverse reactions were experienced by five (12.5%) of the 40 patients (one case each of headache, dull headache, pain in the posterior region of the neck, heartburn, stomach discomfort, and anemia), but all were mild and resolved without treatment. Beraprost sodium was shown to improve API and symptoms in the lower extremities in diabetic patients with ASO, suggesting that it is useful in treating peripheral circulatory disorders in such patients.