We investigated the mechanism of EDHF-mediated dilation to bradykinin (BK) in piglet pial arteries. Topically applied BK (3 μmol/l) induced vasodilation (62 ± 12%) after the administration ofN ^ω-nitro-l-arginine methyl ester (l-NAME) and indomethacin, which was inhibited by endothelial impairment or by the BK₂ receptor antagonist HOE-140 (0.3 μmol/l). Western blotting showed the presence of BK₂ receptors in brain cortex and pial vascular tissue samples. The cytochrome P-450 antagonist miconazole (20 μmol/l) and the lipoxygenase inhibitors baicalein (10 μmol/l) and cinnamyl-3,4-dyhydroxy-α-cyanocinnamate (1 μmol/l) failed to reduce the BK-induced dilation. However, the H₂O₂ scavenger catalase (400 U/ml) abolished the response (from 54 ± 11 to 0 ± 2 μm; P< 0.01). The ATP-dependent K⁺ (K_ATP) channel inhibitor glibenclamide (10 μmol/l) had a similar effect as well (from 54 ± 11 to 16 ± 5 μm; P < 0.05). Coapplication of the Ca²⁺-dependent K⁺ channel inhibitors charybdotoxin (0.1 μmol/l) and apamin (0.5 μmol/l) failed to reduce the response. We conclude that H₂O₂ mediates the non-nitric oxide-, non-prostanoid-dependent vasorelaxation to BK in the piglet pial vasculature. The response is mediated via BK₂ receptors and the opening of K_ATP channels.