Virulence of phytopathogenic bacteria is often correlated with their ability to produce extraceUular polysaccharides (EPSs). The composition and amount of lipopolysaccharide O-antigens and low molecular weight, cell-associated 13linked glucans may also affect virulence of Gram-negative pathogens. For a few species of Agrobacterium. Clavibacter, Erwinia. Pseudomonas, and Xan­ tlwmonas sufficient biochemical and genetical data has accumulated to permit critical evaluation of possible functions of polysaccharides during pathogene­ sis. It is clear that EPSs are necessary for several pathogens to cause normal disease symptoms such as water-soaking and wilting. Evidence is accumulating that EPSs and ceU-associated polysaccharides also promote colonization and enhance survival of some bacteria within host tissues. Further progress will require the use of thoroughly characterized polysaccharide-minus mutants. "natural" inoculation procedures, and careful monitoring of the fate of bacteria within plants.