FMRFamide-, vasoactive intestinal polypeptide (VIP)-, somatostatin-, substance P(SP)-, cholecystokinin octapeptide (CCK-8)- and pancreatic polypeptide (PP)-like materials were immunohistochemically detected in the endocrine cells and the gut innervation of diapausing pharate and newly-hatched first-instar larvae of Antheraea yamamai. SP- CCK-8-, PP- and FMRFamide-like immunoreactive cells were distributed unequally in different midgut regions; no cells reacting with antisera against VIP and somatostatin were found. Innervation of the anterior region of midgut, close to the foregut-midgut boundary, included 90-100 FMRFamide-like bipolar neurons that project along the midgut longitudinal muscles. No immunoreactive cell bodies were found in the foregut and hindgut, but nerve fibers with FMRFamide-like material were detected in hindgut muscles and extended over the posterior midgut. No changes in the distribution and intensity of immunostaining of both the endocrine cells and the gut innervation were found in four developmental stages between pre-diapause and hatching. SP-, CCK-8-, PP- and FMRFamide-like immunoreactive cells were also found in the CNS, indicating that the corresponding antigens belong to brain-gut regulatory peptides.