The ability of some bacterial strains to obtain iron from ethylenediamine di-o-hydroxyphenylacetic acid (EDDA) or iron-free transferrin, and accordingly grow in their presence, was studied. Growth of Staphylococcus aureus and Yersinia pseudotuberculosis was inhibited by EDDA or by iron-free transferrin. Growth of Streptococcus faecalis, however, was inhibited by iron-free transferrin, but not by EDDA. The other bacterial strains, i.e.; Escherichia coli, Salmonella typhimurium and Shigella dysenteriae were able to grow both in the presence of EDDA or iron-free transferrin. All of the above bacterial strains grow in the presence of iron-saturated transferrin which was not able to bind the iron of the medium and accordingly left the iron of the medium available to them.