The extracellular polysaccharides produced by 17 virulent strains of Pseudomonas solanacearum collected from Japan and USA were compared in terms of wilt-inducing activity on tomato cuttings, sugar compositions, amino sugar content and degree of N-acetylation of the amino sugar. It was found that all polysaccharides investigated had wilt-inducing activity on tomato cuttings and that they were composed mainly of N-acetylgalactosamine residue.