The eclosion hormone (EH) activities which can induce the precocious adult eclosion of the pharate-adults of Bombyx mori or Samia cynthia ricini were present in the adult heads of Pseudaletia separata, Bombyx mori, Samia cynthia ricini, Antheraea pernyi, Antheraea yamamai and Manduca sexta. These results indicated that EH is not a species-specific hormone among the lepidopteran insects.