TAS 205 is an inhibitor of hematopoietic prostaglandin D synthase (H-PGDS; IC50= 55.8 nM).1It is selective for H-PGDS over lipocalin-type PGDS (L-PGDS) at 100 μM, as well as over enzyme and receptor panels at 10 μM. TAS 205 inhibits production of prostaglandin D2induced by A23187 in KU812 human and RBL-2H3 rat basophils with IC50values of 78.3 and 181.3 nM, respectively. It inhibits ovalbumin-induced nasal lavage fluid eosinophil infiltration and late-phase nasal obstruction in an ovalbumin-sensitized guinea pig model of allergic rhinitis when administered at a dose of 30 mg/kg.