In order to investigate the effect of EDTA on the growth of bacteria, EDTA and bivalent metal ion were added to the media in fixed proportion. The growth of Sal. 57 S and Staph. aureus were studied on this madia and the following results were odtained. 1) Sal. 57 S were able to grow on nutrient agar media containing up to 0.008 M EDTA. The rate of growth was the same as the control up to a concentration of 0.006 M EDTA Staph. aureus was able to grow on nutrient agar media containing up to 0.006 M EDTA. The rate of growth of Staph. anreus was the same as to the control up to a concentration of 0.005 M EDTA. 2) After repeated transfers the Sal. 57 S was capable of growing on media containing 0.009 M EDTA. Staph. aureus also showed an ability to grow in higher concentration of EDTA, i. e. 0.0075 M EDTA. The rate of growth of the subcultured organisms mentioned above was the same as the control. However, in higher concentration of EDTA no growth was observed, even with the subcultured organisms. 3) Since the equal mols of EDTA and bivalent ion are equivalent, the excessive mol of EDTA must exist in media in free when mol of bivalent ion was added in smaller amount than mol of EDTA. The auther would express the excessive mol of EDTA as "possible concentration of EDTA". The relationship between “possible concentration of EDTA” and the growth of organisms was studied having chelated EDTA by Mg(++) and Fe(++). By chelation of Mg(++) the rate of growth of Sal. 57 S was proportional to "possible concentration of EDTA" as well as to "true concentration of EDTA", that medned the concentration of EDTA added with no chelation. In the same test using Staph aureus the rate of growth was somewhat inferior than expected rate of growth. However, in chelation by Fe(++) the rate of growth against "possible concentration of EDTA" did not correspond to "true concentration of EDTA", but the rate was exceedingly inferior. 4) The effect of addition of EDTA to peptone water and bouillon was studied. The growth of Sal. 57 S was gradually decreased by the addition of EDTA, but up to a certain concentration no decrease was observed. The growth of Staph. aureus was completely inhibited at concentrations of 0.004-0.005 M EDTA, but only small concentration was nescessary for partial inhibition. The rate of growth of EDTA resistant bacteria was superior than normal bacteria. 5) The rate of growth of bacteria to a "possible concentration of EDTA" was superior than the rate of growth to a "true concentration of EDTA". The rate of growth mentioned above was observed in peptone water and bouillon media chelating by Mg(++). 6) By contrast, normal Sal. 57 S and EDTA resistant Sal. 57 S on metal ion free synthetic media the EDTA resistant bacteria showed marked growth with the addition of only a small amount of Mg(++).