Lactic acid bacteria (LAB) and bioactive peptides from these LAB are known to have antitumoral properties⁽ Reference LeBlanc, Matar, Valdez, LeBlanc and Perdigon ^{1 )}, although the intrinsic mechanisms responsible for the execution of this activity are poorly understood. Previous work in our laboratory reported that concentrated supernatants from L. plantarum reduce the development of HL-60 cells and increase the erythrocyte hemolysis⁽ Reference Puertollano, Puertollano, Cruz-Chamorro, Álvarez de, Ruiz-Bravo and de Pablo ^{2 )}. Here we investigated the ability of concentrated supernatants from L. plantarum to promote cell death in this human promyelocytic cell line. This study was aimed to test the hypothesis that concentrated supernatants from L. plantarum at 5, 50 or 100 μg/ml for 24 h exert cytotoxic effects on HL-60 cells. Accumulation of reactive oxygen species (ROS) was diminished and nuclear staining with Hoechst 33342 and propidium iodide (PI) determined a necrotic induction in a concentration-dependent sequence. Concentrated supernatants did not modify or reduced the activity of caspase-3. The assessment of phosphatidylserine externalization by annexin V/PI double staining led to a necrotic state, but the treatment did not produce a dissipation of mitochondrial membrane potential (Δψm), whereas cell cycle analysis revealed that concentrated supernatants failed to significantly enhance the population of HL-60 cells in the hypodiploid (sub-G1) fraction. In this study we demonstrated the cytotoxic properties of concentrated supernatants from L. plantarum on a tumour cell line, and then, to open the possibility to analyze the chemical composition to elucidate the bioactive molecules.