systemic acquired resistance (sar) confers long-lasting protection against a secondary infection by biotrophic, necrotrophic and hemibiotrophic pathogens. sar is a two steps process. firstly, the plant recognizes the pathogen and induces a local plant response through a signal cascade that ends in an intracellular salicylic acid (sa) accumulation. this accumulation induces an increase in reactive oxygen species (ros) and expression of pathogenesis related (pr) genes. secondly, this local response induces a long distant resistance to pathogens in uninfected tissue. it has been postulated that molecules such as methyl salicylate (mesa), some mapks and nitric oxide (no), among others, could be responsible for the induction of sar in the systemic tissue. during sar there is a big interaction among sa, ja, auxins, ethylene and npr1 and pr1 proteins. this review describes the last understanding about the molecular signalling to induce sar trough sa.