AH 6809 is an EP and DP receptor antagonist with nearly equal affinity for the cloned human EP1, EP2, EP3-III, and DP1 receptors. AH 6809 blocks the PGE2-induced accumulation of cAMP in COS cells transfected with the human EP2 receptor. It also blocks the accumulation of Ca2+ in Xenopus oocytes expressing the human EP1 receptor. In the human and guinea pig, the activity profile of AH 6809 is similar to that of SC-19220, but it is somewhat more potent. In the mouse, AH 6809 has the highest affinity for the EP2 receptor, but also acts as a weak ligand at the murine EP1 and DP1 receptors. In whole human platelets, AH 6809 is an effective antagonist of the antiaggregatory actions of PGD2, but not PGI2, with an EC50 of about 5 x 10−5 M.