Molting processes are controlled by ecdysteroids produced by a pair of Y-organs (YOs). Cytochrome P450 enzymes convert cholesterol to a polyhydroxylated product (ecdysone), which is hydroxylated to the active hormone, 20-hydroxyecdysone (20E), by peripheral tissues. The YO transitions through four physiological states over the molt cycle; these are designated basal (intermolt), activated (early premolt), committed (mid premolt), and repressed (postmolt). YO activation requires mTOR activity. Two-dimensional gel electrophoresis and matrix-assisted laser desorption ionization tandem time-of-flight (MALDI-TOF/TOF) mass spectrometry were used for proteomic analysis of the YO over the molt cycle. Analysis of the Carcinus maenas proteome showed expression of anti-reactive oxygen species (ROS) proteins (e.g., superoxide dismutase, catalase, peroxidoxin 3, cyclophilin A) that neutralize oxygen radicals likely produced from ecdysteroid biosynthesis; a transaldolase that regulates ecdysteroidogenesis; and a glutamate dehydrogenase that links production of α-ketoglutarate to mTOR activation. There were significant changes in protein abundance in the YO in eyestalk-ablated (ESA) and multiple leg autotomy (MLA) molt-induced blackback land crab, Gecarcinus lateralis. 457 proteins were detected in the YO of MLA animals, of which 50% changed significantly in abundance over the molt cycle. Comparatively, 358 proteins were detected in the YO of ESA animals, of which 28% changed significantly in abundance. Principle component analysis shows that the basal, activated, committed, and repressed YOs are discrete states. Further analysis will begin to resolve the cellular changes involved in transition of the YO between physiological states. Supported by NSF (IOS-1257732).