Drosophila, like other insects, responds to the injection of bacteria by the rapid and transient synthesis of a battery of potent antibacterial peptides. Only a few of these peptides have been fully characterized to date. We review our recent data on the control of the expression of a gene encoding one of the induced peptides, i.e. diptericin. Our data highlight the role of proximal cis-regulatory motifs similar to regulatory elements binding NF-kappa B and NF-IL6 in promoters of some immune genes of mammals. We argue that the Drosophila host defense is homologous to the mammalian acute phase response.