BI-671800 is a highly specific and potent antagonist of chemoattractant receptor-homologous molecule on Th2 cells (DP2/CRTH2), with IC50 values of 4.5 nM and 3.7 nM for PGD2 binding to CRTH2 in hCRTH2 and mCRTH2 transfected cells, respectively. BI-671800 has potential for the treatment of poorly controlled asthma.