SUMMARY: The extracellular polysaccharides of seventeen strains (four species) of Rhizobium were studied chromatographically. The seven strains from lucerne (R. meliloti) produced polysaccharides which contained glucose but consistently lacked glucuronic acid. The remaining ten strains, which were isolated from pea (R. leguminosarum), clover (R. trifolii) and bean (R. phaseoli), produced a polysac-charide in which both glucose and glucuronic acid were demonstrated. These latter strains could be grouped into three types according to their glucose: glucuronic acid ratio, but such groups did not correspond with the species.