The molt cycle in decapod crustaceans, including the blue crab, Callinectes sapidus, is supressed by the crustacean hyperglycemic hormone (CHH) neuropeptide family and stimulated by ecdysteroids (Ecds). The Ecds are thought to act on both eyestalk ganglia (ES) and Y-organs (YO) where the CHH neuropeptides and Ecds are synthesized, respectively. Since the resultant responses of Ecds are mediated through their nuclear receptors: ecdysone receptor (EcR) and retinoid-X receptor (RXR), the temporal expression of EcR-RXR in ES and YO during the molt cycle may reveal the regulatory role of Ecd on the activity of these two organs. In this study, the full-legnth cDNA sequences of C. sapidus EcR1a and RXR1, and the coding region of three other isoforms of EcR and RXR, were isolated. Moreover, temporal distributions of C. sapidus specific isoforms: CasEcR and CasRXR, were examined in ES and YO at different molt stages