Effects of cilostazol (OPC-13013, CAS 73963-72-1), a selective inhibitor of platelet cAMP-phosphodiesterase, on peripheral vascular disease in diabetes mellitus were studied. Cilostazol in a dose of 200 to 300 mg/d was administered to 5 diabetic patients with arteriosclerosis obliterans. Skin temperature of the finger and the toe, which reflects blood flow to the tissue, was selected as an objective index of cilostazol effects and measured by infra-red thermography at a constant temperature of 26 degrees C. Before administration, digital skin temperatures were low in 9 limbs of 5 patients. 200 mg/d of cilostazol significantly (p less than 0.001) increased the digital skin temperatures of 8 limbs, the increase (mean +/- SD) ranging from 29.9 +/- 1.4 degrees C to 33.2 degrees C +/- 1.2 degrees C for the average skin temperatures and from 28.7 +/- 2.1 degrees C to 33.1 +/- 1.5 degrees C for the lowest ones. An increase in the dose to 300 mg/d resulted in further elevation of skin temperatures of the digits. Cilostazol constantly elicited an increase in blood flow to the digits within the range of its therapeutic dose. This effect was observed about 1 month after initiation of administration and persisted while administration was continued. The measurement of digital skin temperatures by infrared thermography provided a noninvasive means to individualize the dosage of cilostazol and to monitor the cilostazol effect and patient complicance during long-term administration. It is concluded that cilostazol exerts a potent and steady vasodilatory effect on peripheral circulation in patients with diabetes mellitus.