Pseudomonas fluorescensis an emerging pathogen closely related toPseudomonas aeruginosa. In the present study, the effect of thelipopolysaccharide (LPS) fromP. fluorescensMF37 was investigated using indicators of apoptosis and necrosis and was compared to theeffect of the LPS fromP. aeruginosaPAO1. Capillary electrophoresis analysis of the LPS fromP. fluorescensMF37 revealed the existenceof three forms of the endotoxin and the absence of homology with the LPS fromP. aeruginosa. In neurons and glial cells the LPS fromP. fluorescensinduced major morphological changes including a condensation of the cytoplasmic proteins, a leakage of the cytoplasmiccontent, the formation of blebs on the nuclear membrane and a marked reorganization of the cytoskeleton. In glial cells, the LPS fromP. fluorescensprovoked the migration of phosphatidylserine at the surface of the cytoplasmic membrane, a sign of apoptosis, but this reactionwas associated to an increase in the permeability to propidium iodide characteristic of necrosis. Biochemical studies revealed an importantactivation of an inducible nitric oxide synthase and a release of lactate dehydrogenase, a stable cytosolic enzyme. These results demonstratethat the LPS fromP. fluorescensinduces apoptosis and a concomitant and limited necrosis, reveal the unexpected cytotoxicity of thisendotoxin and provide the first demonstration of the apoptotic effect of a non-aeruginosa Pseudomonason nerve cells.