The currently accepted reproductive cycle of Alaskan female Dungeness crab (Cancer magister) is that females molt and mate during summer and fall, extrude eggs in the fall, and incubate eggs through the winter until larval hatching in May and June. In this cycle, molting and mating are coincident with ovarian maturation. In this study, we quantified circulating concentrations of hemolymph ecdysteroids (molting hormones) in laboratory and field sampled crabs using an enzyme-linked immunosorbent assay (ELISA), for molt status assessment of individuals. Captive female crabs from southeastern Alaska (mean CW = 134.8 mm; n = 48) had a typical crustacean molt cycle profile of circulating ecdysteroids. Concentrations of ecdysteroids were low during intermolt (20.3 ± 0.7 ng/ml), maximal during premolt (1886.5 ± 186.2 ng/ml) 15 days before ecdysis and precipitously declined to low levels (< 90 ng/ml) 5 days prior to ecdysis. The duration of premolt was 150 days. Crabs held in captivity either molted (67%), extruded eggs (7%), or demonstrated no reproductive or molting activity (26%). Peak molting occurred in November for crabs held in the laboratory. Most (98%) of the female crabs sampled (n = 579) in Port Frederick, Alaska during the expected premolt period (May-July), had intermolt ecdysteroid concentrations. The capability to predict ecdysis 150 days prior to ecdysis by measuring ecdysteroid concentrations provides a useful tool to assess the molt status and timing of ecdysis in Alaskan Dungeness crab populations.