Quinotolast (also known as FK021) is an orally active mast cell stabilizer which has a cytoprotective effect on the gastric mucosa. Quinotolast was patented in 1985 by Japanese pharmaceutical company Fujisawa Pharmaceutical Co., Ltd. as an antiallergic and antiulcer agent. In preclinical models, Quinotolast potently inhibited such type I allergic reactions as passive cutaneous anaphylaxis (PCA) and anaphylactic bronchoconstriction in rats by both intravenous and oral dosing. Quinotolast inhibited histamine release from rat peritoneal cells, but it had no antagonistic effect on histamine-, serotonin-, platelet activating factor- or bradykinin-induced cutaneous reactions in rats. Moreover, it was clearly demonstrated that quinotolast and DSCG had a cross tachyphylaxis to inhibit PCA in rats, suggesting that these drugs, at least in part, share the same mechanism of action. Quinotolast caused a significant increase in the mucociliary transport rate in quails. Quinotolast significantly depressed the cough reflex induced by citric acid in normal and bronchitic guinea pigs.