Recently, a series of relatively simple compounds were found to be high-affinity ligands and functional antagonists for the human IP (prostacyclin) receptor. CAY10449 is one of the more potent of these. CAY10449 antagonizes the carbaprostacyclin-induced activation of human neuroblastoma adenylate cyclase, blocking cyclic AMP accumulation in a dose-dependent manner. Likewise, it inhibits the binding of tritiated iloprost to rodent neuroblastoma cells with a Ki value of about 3 nM. Although CAY10449 was not tested in rats, the related compound CAY10441 shows significant analgesic activity in standard antinociceptive assays.