Hypercholesterolemia is associated with decreased nitric oxide (NO) bioavailability and endothelial dysfunction, a phenomenon thought to have a major role in the altered cerebral blood flow evident in stroke. Therefore, strategies that increase endothelial NO production have potential utility. Vascular reactivity of the middle cerebral artery (MCA) from C57BL/6J wild-type (WT) mice, apolipoprotein-E knockout (ApoE(-/-)) mice, and mice treated with the phosphodiesterase inhibitor cilostazol (100 mg/kg) was analyzed using the tension myograph. Contractile responses to endothelin-1 were significantly enhanced in MCA from ApoE(-/-) mice compared with WT mice (P<0.01), an effect absent in cilostazol-treated ApoE(-/-) mice. Acetylcholine-induced relaxation (which is entirely NO-dependent) was significantly impaired in MCA of ApoE(-/-) mice compared with WT mice (P<0.05), again an effect prevented by cilostazol treatment. Endothelial NOS phosphorylation at Ser(1179) was decreased in the aorta of ApoE(-/-) mice compared with WT mice (P<0.05), an effect normalized by cilostazol. Taken together, our data suggest that the endothelial dysfunction observed in MCA associated with hypercholesterolemia is prevented by cilostazol, an effect likely due to the increase in eNOS phosphorylation and, therefore, activity.