The oral anti-allergic effect of KY-556 (N-556) is investigated. N-556 (10-100 mg/kg, p.o.) inhibits dose-dependently the 48-hr homologous passive cutaneous anaphylaxis (PCA) in rats, and the duration of action is longer than that of intravenous Disodium cromoglycate (DSCG). N-556 (20 and 100 mg/kg once a day for 20 consecutive days, p.o.) tends to inhibit the histamine release from actively sensitized rat lung fragments. N-556 (100 mg/kg, p.o.) shows the prolongation of survival time in the rat systemic anaphylaxis. N-556 (100 mg/kg, p.o.) significantly inhibits the increased airway resistance in experimental asthma in rats.