Abstract: The anti-anaphylactic action of potassium channel openers was studied and reported in this paper. Minoxidil(Min) was shown to inhibit passive cutaneous anaphylaxis in rats. Diazoxide(Dia) and Min were found to inhibit antigen-induced guinea-pig ileum smooth muscle contraction in vitro. Min was shown to antagonize 5-HTinduced capillary permeability in rat skin. Dia was demon-strated to inhibit histamine release from rat peritoneal mast cells induced by A₂₃₁₈₇ and compound 48/80, but it failed to antagonize guinea-pig ileum smooth muscle contraction induced by histamine in vitro. These results provide evidence that potassium channel openers may be a new group of inhibitors of histamine release and indicate that the mechanism of its anti-anaphylactic action may be related to its potassium channel opening effect. As a result of this effect, Ca²⁺ influx to the mast cells decreases and Ca²⁺ release from calcium storage was inhibited, thus inhibting histamine release.