Summary: The objective of this study is to explore if immunohistochemical and morphological changes occur in crustacean hyperglycemic hormone (CHH, Pej-SGP-III)-and molt-inhibiting hormone (MIH, Pej-SGP-IV)- producing cells during molt stages. Consecutive sections prepared from immature female eyestalks at different molt stages were stained immunohistochemically. Neurosecretory cells producing each of Pej-SGP-III (Pej-SGP-III cells, CHH cells) and Pej-SGP-IV (Pej-SGP-IV cells, MIH cells) were located in the same cluster, the medulla terminalis ganglionic X-organ (MTGX). Neurosecretory cells, which were stained with both anti-Pej-SGP-III and anti-Pej-SGP-IV antiserum (Pej-SGP-III-IV cells), were present. The shape of Pej-SGP-III cells was indistinguishable from that of Pej-SGP-IV cells. The type, mean diameter, number and the staining density of these immunoreactive cells did not change throughout the molt cycle. These findings imply that Pej-SGP-III and Pej-SGP-IV were produced steadily and irrespective of the molt stages.