1. Agonists for protease-activated receptor-2 (PAR-2) cause hypotension and an increase in gastric mucosal blood flow (GMBF) in vivo. We thus studied the mechanisms underlying the circulatory modulation by PAR-2 activation in vivo, especially with respect to involvement of endothelium-derived hyperpolarizing factor (EDHF). 2. Arterial blood pressure and GMBF were measured in anesthetized rats in vivo. Vascular relaxation was assessed in the precontracted rat gastric arterial rings in vitro. 3. The PAR-2-activating peptide SLIGRL-NH2 and/or trypsin, administered i.v., produced largely NO-independent hypotension and increase in GMBF accompanied by decreased gastric mucosal vascular resistance (GMVR) in rats. 4. Combined administration of apamin and charybdotoxin, but not each of them, specifically abolished the hypotension, increased GMBF and decreased GMVR caused by the PAR-2 agonists. 5. In the isolated rat gastric artery, SLIGRL-NH2 elicited endothelium-dependent relaxation even in the presence of an NO synthase inhibitor and indomethacin, which was abolished by apamin plus charybdotoxin. 6. Our data suggest involvement of apamin/charybdotoxin-sensitive K+ channels in the PAR-2-triggered hypotension and increased GMBF, predicting a role of EDHF-like factors.