To investigate whether NO production in mouse macrophages contributes to S. Typhimurium virulence, RAW264.7 cells were treated with L-NMMA, a competitive inhibitor of iNOS, 2 h prior to infection to inhibit NO production, and the expression of SPI-2 genes in treated and non-treated cells was assessed at various time points during the infection period. This evidence concerns the gene NOS2 and infection.