There were at least two kind of cytolytic substances on Ehrlich ascites carcinoma cells in the culture medium of Bacillus natto KMD 1126. One was adsorbed on carbon, eluted with EtOH, and large molecule by Sephadex G 25 gel filtration, but the other was not adsorbed on carbon and small molecule by Sephadex G 25 gel filtration. The former was stable on wide range of pH and temperature. This cytolytic substance was isolated and its chemical structure was examined by elementary analysis, infrared spectrum, nuclear magnetic resonance, and mass spectroscopy and study of decomposed products. As the results, the cytolytic substance was proved to be identical with surfactin which was potent coltting inhibitor in the thrombin fibrinogen system obtained from culture medium of Bacillus subtilis by Kakinuma, et al.
