Mammalian ferritin subunit synthesis is controlled at the translational level by the iron regulatory protein 1 (IRP1)/iron responsive element (IRE) interaction. Insect haemolymph ferritin subunit messages have an IRE in the 5'-untranslated region (UTR). We have shown that recombinant M. sexta IRP1 represses the in vitro translation of both the heavy and light chain ferritin subunits from this species without altering transcription. Deletion of either the 5'-UTR or the IRE from the mRNA abolishes IRP1 repression. Our studies indicated that the translational control of ferritin synthesis by IRP/IRE interaction could occur in insects in a manner similar to that of mammals. To our knowledge, this is the first report of the control of insect ferritin synthesis by IRP1/IRE interaction. Furthermore, this is the first indication that the synthesis of a secreted ferritin subunit can also be controlled in this manner.