A polysaccharide, being an active inductor of gamma-interferon, has been found among glycopolymers of Clavibacter michiganense. Lipopolysaccharide of Pseudomonas solanacearum is shown to display an interferonogenic activity which is analogous to that of the classical interferon inductor, lipopolysaccharide of Escherichia coli O55: B5. Besides lipid A, core oligosaccharide also contributes much to the interferonogenic activity of P. solanacearum lipopolysaccharide.