| Summary: | Sliced ready-to-eat meat products packaged under modified atmospheres are often marketed since they cover consumer demands. The slicing process could be a potential risk for consumers since contamination with <i>Listeria monocytogenes</i> could occur during this stage. The current study evaluated the behavior of <i>L. monocytogenes</i> and other microorganisms in commercial sliced Riojano chorizo. This meat product was sliced and inoculated with <i>L. monocytogenes</i> (3.5 log CFU/g) before packaging under different atmospheres (air, vacuum, 100% N<sub>2</sub>, 20% CO<sub>2</sub>/80% N<sub>2</sub> and 40% CO<sub>2</sub>/60% N<sub>2</sub>) and stored at 4 °C for up to 60 days. Samples were taken on days 0, 7, 21, 28 and 60 of storage. <i>L. monocytogenes</i>, mesophiles, <i>Enterobacteriaceae</i>, lactic acid bacteria, <i>Micrococcaceae</i>, molds and yeast counts were evaluated. Additionally, water activity, humidity and pH were determined. <i>L. monocytogenes</i> counts decreased in inoculated sliced chorizo during storage. Packaging conditions and day of storage influenced microbial counts. After 60 days, a significant reduction (<i>p</i> ≤ 0.05) in the initial <i>Listeria</i> contamination levels (3.5. log CFU/g) between 1.1 and 1.46 logarithmic units was achieved in the sausages packaged in modified atmosphere. The highest reductions were observed in slices packaged in 40% CO<sub>2</sub>/60% N<sub>2</sub> after 60 days of storage at 4 °C.
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