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 en- dothelial cell cultures to native or oxidized low density lipoproteins,low density lipoproteins treated by dimethylsul- foxide-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 or endothelin-1 (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 or vasoconstrictor activity in conditioned medium from bovine aortic EC is endothelin-1. Objective To study the releases of endothelin-1 and prostacyclin by endothelial cells in culture and to elucidate how these releases were detected by smoke-treated low density lipoprotein. Methods We exposed en- dothelial cell cultures to native or oxidized low density lipoproteins, low density lipoproteins treated by dimethylsul- foxide-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 or endothelin- 1 (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 or vasoconstrictor activity in conditioned medium from bovine aortic EC is endothelin-1 .