Genomic and proteomic approaches were applied to characterize the immunoproteome of Heliothis virescens. Larval hemocytic responses to bacterial and baculoviral infection were surveyed using expressed sequence tags (ESTs). 5349 ESTs formed 429 contigs, 258 singlets and 1104 singletons, totalling 1791 putative transcripts. Of these putative transcripts 1248 BLAST to immune response, structural, mitochondrial, and metabolic enzyme homologs of other insect species. Many hemocytic transcripts of known or putative immune function were identified, e.g., zymogen prophenoloxidases (PPOs), enzymes of the PPO activating pathway, and C-type lectins. Digital gel electrophoresis of plasma proteins induced by infection followed by MS/MS of tryptic peptides revealed upregulation of many of the same proteins identified among ESTs, i.e. PPO and components of the PPO activating pathway. These complementary proteomic and genomic approaches indicate that bacterial but not baculoviral infection upregulate PPO and its activation pathway. The response of other innate immune response components to infection will be discussed.