Gene-encoded peptide antibiotics are widespread in insects, plants and vertebrates and confer protection against bacterial and fungal infections. NF-κB is an important transcription factor for many immunity-related mammalian proteins and also for insect immune genes. The activity of NF-κB is regulated by the interaction with an inhibitor, IκB. It was recently demonstrated that glucocorticoids induce the synthesis of IκB in human cell lines. So far, all genes for peptide antibiotics have promoter motifs with NF-κB binding sites, but its actual function in peptide regulation has been studied only in insects. Here we show that glucocorticoid treatment of the frog Rana esculenta inhibits the transcription of all genes encoding antibacterial peptides by inducing the synthesis of IκBα. These results suggest that also in vertebrates peptide-mediated innate immunity is controlled by NF-κB-regulated transcription.