Ralstonia solanacearum is one of the most devastating phytopathogenic bacteria, in particular its race 3. This microorganism is the causal agent of destructive diseases of different crops including tomato and potato. An important aspect of the interaction between this pathogen, and the host and non-host plants was its biochemical and molecular basis. Thus, the lipopolysaccharides (LPS) were extracted from the R. solanacearum cell wall, purified, and the O-specific polysaccharide (OPS) was isolated and chemically characterized by compositional analyses and NMR spectroscopy. The OPS was constituted of two linear polymers of an approximate ratio of 3 : 1, both of which were built up from three rhamnose and one N-acetylglucosamine residues and differed only in the substitution of one rhamnose residue. The LPS inhibited the hypersensitivity reaction (HR) in non-host tobacco plants and induced localized resistance in host potato plants, both of which were pre-treated with the LPS before being inoculated with the pathogen. A cDNA-AFLP approach was used to study transcriptome variation during the resistant and susceptible interactions. This revealed the presence of metabolites specifically expressed in the S. commersonii-resistant genotypes, which could be involved in the plant-pathogen incompatible reaction. Furthermore, a specific EST collection of the Ralstonia-potato interaction has been built up.