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Actinobacillus suis' is a Gram-negative bacterium emerged as a swine pathogen in young and adult pigs causing various clinical syndromes and death seriously affecting the swine industry. Despite the growing demand a serological test and vaccine are not yet available on the market. These aids could be produced using the unique surface polysaccharides produced by the bacterial cells. Work has already been started in our laboratory to establish a thorough lipopolysaccharide O antigen (0) and capsule polysaccharide (K) serotyping system and develop a multivalent vaccine against 'A. suis.' As previously reported serovar O1 strains (ATCC 15557, B49, SO4, H93-055) express an O and K antigen with a (1[right arrow]6)-[beta]-D-glucan that is similar in structure to a key cell wall component in yeasts. The O2 antigen [Gal[right arrow][Gal[right arrow]]-Glc[right arrow]GlcNAc] n of 'A. suis' strain H91-0380 was also described earlier. Continuing our research towards the development of a serotyping system and a multivalent vaccine, the structure of a common oligosaccharide expressed by several 'A. suis' strains (VSB 3714, ATCC 15557, H91-0380, C84) was characterized. Its backbone is built up by alternating units of galactose and partially O-acetylated N-acetylglucosamine residues completed with sialic acid and phosphoethanolamine side branches:* The K2 capsular polymer of strains C84 and H91-0380 were also analyzed and described here. It has a [[right arrow]O-POOH-O[right arrow]4)-[beta]-GlcNAc,3OAc-(1[right arrow]3)-[alpha]-Gal-(1[right arrow]] n, backbone structure with non stoichiometric fructosylation at C2 of the galactose residue. The occurrence of the (1[right arrow]6)-[beta]-D-glucan capsule in strain VSB 3714 was also established and finally the structure of the O2 antigen (strain H91-0380) was revised and corrected. *Please refer to dissertation for diagrams.