L-657926 is a stereoselective antagonist of the thromboxane A2 (TxA2) receptor, composed of (-)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-1-yl acetic acid and (+)-9-chlorobenzyl-6-fluoro-1,2,3,4-tetrahydrocarbazol-l-yl acetic acid. The IC 50 s of (-) and (+) configurations for TxA2 are 0.27 nM and 124 nM, respectively.