Bacillus natto KMD 1126 suspension had not remarkable cytolytic activity on Ehrlich ascites carcinoma cells. But when the bacterial suspension was preincubated in the buffer at 37°for 2 hr, cytolytic substances were found out of the cells. These results were observed by eosin stain method, measurement of cell injuring activity and in vitroin vivo test. It was observed that the formation of cytolytic substances were intimately related with bacterial growth phase, and bacterial cells at logarithmic phase and early stationary phase made much amounts of the substances, and cells at lag phase could not form it. On the other hand, it was observed that there are at least two kind of cytolytic substances in the preincubation mixture by Sephadex G 25 gel filtration. One, which is high molecule, had cytolytic and hemolytic activities, but the other, which is low molecule, had cytolytic activity only.
