A putative capsular polysaccharide containing D-rhamnose was isolated from the phytopathogenic bacterium Burkholderia gladioli pv. agaricicola by phenol/water extraction followed by ultracentrifugation of the separated water phase and gel-permeation chromatography of the thus obtained supernatant. By means of chemical analyses and NMR spectroscopy, the repeating unit of the polymer was shown to be a linear tetrasaccharide with the structure. [carbohydrates: see text].