Objective To study the releases of endothelin-1 and prostacyclin by endothelial cells in culture and to elucidate how these releases were influenced by smoke-treated low density lipoprotein. Methods We exposed endothelial cell cultures to native or oxidized Iow density lipoproteins,low density lipoproteins treated by dimethylsulfoxide-soluble particles from cigarette smoke or dimethylsulfoxide alones. The release of endothelin-1 was assayed by bioassay and the release of prostacyclin was assayed by radioimmunoassay. Results Low density lipoproteins treated by smoke significantly increased the release of endothelin-l (P＜0. 025) and decreased the release of prostacyclin (P＜0. 02) by endothelial cells in culture, contrast to native or dimethylsulfoxide-treated lipoproteins. Conclusion The main part of vasoconstrictor activity in conditioned medium from bovine aortic EC is endothelin-1.