Hemolin, a protein of the immunoglobulin superfamily, is expressed in several organs of Galleria mellonella, including the silk glands. Constitutive expression of the hemolin gene in the whole silk gland is enhanced upon injection of bacteria or their components, the peptidoglycans and lipopolysacharides. Gene expression rises in the post-feeding larvae and culminates during cocoon spinning. Application of 20-hydroxyecdysone to isolated larval abdomens causes a similar enhancement of gene expression but it is curbed by simultaneous administration of a juvenile hormone mimic. In vitro experiments showed that the action of hormones on the hemolin gene expression in silk glands is not mediated by other organs. Hemolin protein is deposited in the cocoon and larval silks.The work was in part supported by grant A5007402 from the Grant Agency of the Academy of Sciences.