Trichomonas vaginalis has high iron-dependency, favoring its growth and multiplication in culture. Iron also regulates some of the trichomonal virulence properties by yet unknown mechanisms. Iron is an essential but potentially toxic metal for the majority of organisms. Thus, its concentration must be tightly regulated within the cell. In mammals, the iron homeostasis is mainly regulated at the post-transcriptional level by a well known mechanism mediated by the binding of iron regulatory proteins (IRP1 and IRP2) to hairpin-loop structures, dubbed iron-responsive elements (IREs), localized in the untranslated regions (UTRs) of target mRNAs. The knowledge of iron regulation in T. vaginalis is still very limited. An iron-responsive promoter and other regulatory elements in the 5'-UTR of the ap65-1 gene were identified as a mechanism for the positive transcriptional regulation of trichomonad genes by iron. Recently, two IRE-like hairpin-loop structures in mRNAs of differentially iron-regulated TVCP4 and TVCP12 cysteine proteinases, as well as IRP-like trichomonad proteins were identified in T. vaginalis, suggesting the existence in this protozoan of a post-transcriptional iron regulatory mechanism by an IRE/IRP-like system. The responsiveness of T. vaginalis to distinct iron concentrations was examined here. Also, the comparison of the atypical IRE-like sequences of T. vaginalis with the consensus IRE and other putative IRE sequences present in parasite and bacteria mRNAs suggest that these trichomonad IRE-like sequences might be the ancestral forms of the RNA stem-loop structures of the IRE/IRP system.