We demonstrated that up-regulation of gene expression of endoplasmic reticulum (ER) chaperones (BiP, calnexin, calreticulin, ERp29) and ER membrane kinases (IRE1, PERK, ATF6) was induced by radiation in neuronal PC12 cells. However, addition of silkworm, Bombyx mori, hemolymph to irradiated cells resulted in an obvious decrease in expression of these genes, compared with a single radiation treatment. In contrast, one of the ER chaperones, "ischemia-responsive protein 94 kDa" (irp94), was up-regulated by radiation. However, addition of silkworm hemolymph resulted in no change in the expression of irp94, with an expression pattern that differed from that of ER chaperones. Based on these results, we propose that silkworm hemolymph contains factors that regulate a decrease in the expression of ER chaperones under radiation-irradiation conditions, with the exception of irp94, which is not down-regulated. We suggest that this difference in the molecular character of irp94 may provide a clue to the biological functions associated with ER stress pathways, particularly the effects of radiation.