Silk gland cells of silkworm larvae undergo multiple endomitotic cell cycles for the synthesis of silk proteins in the spinning phase.Here we analyze the endomitotic DNA synthesis of the silk gland cells during the larval ontogeny.The endomitotic DNA synthesis exhibits a periodic fluctuation during the larval stages.In particular,the activity of the DNA synthesis is the maximum during the fifth intermolt stage.The expression levels of cyclin E,CDT1 and PCNA are consistent with the developmental change of the DNA synthesis.Moreover,the possible endomitotic cellar mechanism causing the activation of the endomitotic DNA synthesis in the intermolt stages owes to feeding with fresh mulberry and the inhibition of the DNA synthesis during the molting stages owes to the hormones is further examined.Our results indicate that the activation of the endomitotic DNA synthesis during the intermolt stages is related to feeding and the DNA synthesis is inhibited indirectly by 20-hydroxyecdysone.