OBJECTIVE Prostacyclin, which is mainly synthesized by vascular endothelial cells, exerts antiplatelet and smooth-muscle-relaxant effects, thereby maintaining cardiovascular homeostasis. Prostacyclin analogues have been clinically proven to improve ischemic symptoms and prevent the occurrence of vascular events in the lower extremities of patients with arteriosclerosis obliterans. We examined the presence of prostacyclin receptor (IP receptor) in an arteriosclerotic human femoral artery. METHODS Specimens of the femoral artery were obtained at the time of limb amputation from an 83-year-old woman. Atherosclerotic lesions and associated changes such as calcification were evident. The specimens were stained with hematoxylin and eosin, and processed for immunohistochemistry. RESULTS A monolayer of cells was observed on the luminal side of the femoral artery. Single immunohistochemistry showed the presence of the IP receptors on cells of the luminal side of the femoral artery. Triple-immunofluorescence staining revealed colocalization of IP-receptor-positive cells and cells positive for von Willebrand factor, a marker of vascular endothelial cells. CONCLUSIONS We investigated the presence of the IP receptor in the human femoral artery immunohistochemically, and demonstrated their strong expression in endothelial cells. This finding suggests that prostacyclin or prostacyclin analogues may act on their receptors on endothelial cells in patients with arteriosclerosis obliterans.