An adipokinetic hormone (AKH) was isolated from the adult heads of the silkworm, Bombyx mori. Fast atom bombardment mass spectrometry (FAB-MS) of the intact AKH and sequence analysis of the AKH after deblocked with pyroglutamate aminopeptidase revealed that the structure of Bombyx AKH is pGlu-Leu-Thr-Phe-Thr-Ser-Ser-Trp-Gly-NH2, which is identical with those of Manduca sexta and Heliothis zea AKH. Bombyx AKH is released just after adult eclosion and elevates the lipid level but not the carbohydrate level in the hemolymph.