The biological effects of PGD2 (Item No. 12010) are transduced by at least two 7-transmembrane G protein-coupled receptors, designated DP1 and DP2/CRTH2. BAY u3405 (Ramatroban) is an approved human medication for the treatment of allergic rhinitis that has documented activity as an antagonist of the TP receptor.{12335} BAY u3405 is also an antagonist of the DP2 receptor with IC50 values of 100-170 nM.{11248} BAY u3405 is more potent at the DP2 receptor than the TP receptor by 4-5 fold. BAY u3405 is therefore a useful tool for the elucidation of PGD2/DP2 function in eosinophils, basophils, and other cells of the TH2 cell-type.