The compound (+) {7R-[[(4-fluorophenyl)sulfonyl] (methyl)ammo]-6,7,8,9-tetrahydropyrido[1,2-a]mdol-10-yl}acetic acid and pharmaceutically acceptable salts thereof are antagonists of the PGD2 receptor, CRTH2, and as such are useful in the treatment and/or prevention of CRTH2-meidated diseases such as asthma.