Summary: Iron restriction was induced in Escherichia coli O111, E. coli O164 and E. coli C by growing the organisms in trypticase soy broth containing ovotransferrin, desferal, EDDA (ethylenediamine-dihydroxyphenylacetic acid) or α,α'-dipyridyl. There were marked qualitative and quantitative differences in the iron regulated outer membrane proteins expressed in the presence of the various iron chelators. Differences in the kinetics of growth were also noted. E. coli C was devoid of a ferric enterobactin iron uptake system.