The typical dark brown stripe symptom of bacterial wilt disease was observed in the cuttings of tobacco stem treated with the culture filtrate of virulent Pseudomonas solanaceamm. And the tobacco callus create.4 with that culture filtrate showed deterioration of the callus 2 days after the treatment. On the contrary, the cuttings and the callus treated with the culture filtrate of the avirulent bacteria expressed no typical symptom and vigorous growth respectively. Therefore it was suggested that certain toxin which might be produced by the virulent bacteria could break down tobacco cells.