Disclosed herein are 3-(heteroaryl-amino)-1,2,3,4-tetrahydro-9H-carbazole derivatives of the formula (I), wherein R1, R2 and R3 are as described in the description and their use as prostaglandin receptor modulators, most particularly as prostaglandin D2 receptor modulators, in the treatment of various prostaglandin-mediated diseases and disorders, to pharmaceutical compositions containing these compounds and to processes for their preparation. In one embodiment the compound is (3S)-2-(6-fluoro-3-((5-fluoropyrimidin-2-yl)amino)-3,4-dihydro-1H-carbazol-9-(2H)-yl) acetic acid.
