On the basis of vascular involvement, an open clinical trial was performed to determine whether or not the antithrombotic drug cilostazol (6-[4-(1-cyclohexyl-1H-tetrazol-5-yl) butoxy]-3,4-dihydro-2(1H)-quinolinone, OPC-13013, Pletaal, CAS 73963-72-1) applied as a single 100 mg tablet increases peripheral blood flow and prevents diabetic neuropathy in 30 patients with non-insulin dependent diabetes mellitus. The hemodynamic effects of this drug on the a. dorsalis pedis were examined using a new real-time two-dimensional Doppler echography. 1 h after oral administration of cilostazol, the cross-sectional area of the a. dorsalis pedis significantly increased from 2.2 +/- 0.2 to 2.9 +/- 0.3 mm2 (p less than 0.05). Also, the a. dorsalis pedis blood flow index significantly increased from 16 +/- 1 to 31 +/- 4 (p less than 0.05). Cilostazol did not affect plasma glucose level (from 213 +/- 14 to 198 +/- 15 mg/dl), but slightly plasma ratio of 6-keto PGF1a to TXB2 (from 0.71 +/- 0.09 to 0.83 +/- 0.12). These effects of cilostazol might ameliorate diabetic neuropathy by improving blood flow and preventing nerve tissue ischemia.