1. The abnormally elongated filament cell formafion was observed on Mitomycin C containing agar in 1 gamma per ml. In the filment cells, by cell wall staining method, no septum formation was observed notwithstanding cell wall structure was retained. By a method of chromatinic body staining, regularly arranged abundant chromatinic bodies were observed. 2. By a method of manometric technique, the filament cells exhibited low oxidation activities to the substrates on TCA cycle. 3. With respect to acid agglutination test, the filament cells were agglutinated at the different range as compared with normal cells. 4. In the course of the filament formation, RNA synthesis proceeded without inhibition but DNA synthesis was slightly inhibited.