Acyl-CoA-binding protein (ACBP), also known as the diazepam-binding inhibitor (DBI), has been identified in diverse species and is evolutionarily conserved in plants and animals. In a recent study, an ACBP cDNA (HaACBP) encoding 85 amino acids was isolated from the cotton bollworm Helicoverpa armigera. The isolated protein is highly homologous to the ACBP present in the Bombyx mori midgut, where it is highly expressed. Northern and Western blot analyses revealed that HACBP is expressed predominantly in the midgut. Moreover, Northern blotting revealed that HaACBP was probably stimulated by a high juvenile hormone titer at ecdysis and increased along with feeding at 12 h post-ecdysis. Immunohistochemistry of the midgut revealed that HaACBP is localized in columnar cells. Data from the Northern blotting and immunohistochemistry suggested that HaACBP was expressed during the larval period and is probably responsible for nutrition absorption. However, Western blot analysis of the midgut at different developmental stages indicated that HaACBP was upregulated during larval molting and metamorphosis, which suggested that HaACBP expression was posttranscriptionally regulated.