We report here the use of a specific beta-galactosidase staining assay and Northern blotting technique to examine the expression of three genes encoding either antibacterial peptides (diptericin, cecropin A) or an antifungal peptide (drosomycin) in Drosophila following infection by larval and pupal parasitoids. The results show that the genes encoding these peptides are either not induced or minimally induced in wasp-infected hosts, but remain responsive and are induced upon microbial challenge. As the parasitoids elicit a cellular response, our data suggest that the antimicrobial responses are activated and/or regulated by mechanisms that are independent of those mediating cellular encapsulation.