The pharmacological properties of KP-136 were studied using cutaneous reactions in rats and guinea pigs. KP-136 remarkably inhibited the passive cutaneous anaphylaxis (PCA) with intravenous and oral dosing. However, the inhibitory effect of KP-136 had an apparent species difference. Thus, KP-136 was more effective on rat PCA than that of guinea pig. In four rat cutaneous reactions produced by three allergic reactions and compound 48/80, KP-136 was remarkably effective on two homologous PCA induced by IgE and IgGa. The intravenous and oral doses for 50% inhibition on the PCA were 0.2 mg/kg to 0.4 mg/kg and 0.5 mg/kg to 0.9 mg/kg, respectively. KP-136 was scarcely effective on cutaneous reactions elicited by intradermal injection of histamine and serotonin which are main chemical mediators in rat homologous PCA. However, KP-136 blocked the degranulation of mast cells and decrease of histamine content in skin elicited by the PCA. In addition, KP-136 showed a potent inhibition on the immunological release of histamine from rat peritoneal exudate cells. The concentration for 50% inhibition on the histamine release was 5 ng/ml. These findings indicate that KP-136 is an oral potent inhibitor on PCA, and it acts by blocking the release of chemical mediator(s) from mast cells.