Induction of apoptosis by the citotoxic active principle of Espeletia killipiiCuatr. on human cell lines".Longipilin acetate is the compound exhibiting cytotoxicity, isolated from endemic plant specie from Colombia, South America, Espeletia killipii Cuatr.Longipilin acetate is a sesquiterpenelactone having the ability to induce apoptosis in several breast cancer cell-lines like MCF-7 y CSC-1595 (obtained from National Cancer Institute, Bogotá Colombia), Morphological examination, nuclear DNA fragmentation, tunel and fl ow cytometry were used to evaluate apoptosis.Therefore longipilin acetate is a compound showing potential as an antitumor agent.