The present study utilizes a newly synthesized TXA2/PGH2 mimetic, I-BOP, to characterize the TXA2/PGH2 receptor in suspensions of cultured human vascular smooth muscle cells. [125I]-BOP bound in a saturable and specific manner (Kd = 2.6 +/- 0.6 nM; Bmax = 33,540 +/- 6,200 sites/cell; 69 fmoles/mg protein, n = 12). Competition binding assays were performed with [125I]-BOP and the TXA2/PGH2 receptor antagonists SQ29548, L657925 and L657926 and the receptor agonist U46619. I-BOP induced concentration-dependent increases in intracellular free calcium which were inhibited by SQ29548. The results provide radioligand binding evidence for the presence of a TXA2/PGH2 receptor in human vascular smooth muscle cells.