Abstract The effect of cadmium on molting of the estuarine crab Chasmagnathus granulata was assayed. Adult males were eyestalk-ablated, in order to synchronically induce molting, and were then chronically exposed to cadmium at 0.25 or 0.50 mg/l. At the highest concentration, a significant mortality was detected at the time of molting, in the few crabs that could reach the E stage. However, most of the crabs exposed from the beginning of the premolt period (D 0 stage) to 0.50 mg/l of cadmium were arrested at the D 1″ stage. This effect was not seen when crabs were exposed to the same cadmium concentration from either D 1‴ or D 3 premolt stages. Crabs arrested by cadmium did not present any difference in the calcium content of carapace, compared to controls, while ecdysteroid levels of those crabs were similar to the ones of control crabs that were in the same premolt stage but could finally molt. These results suggest that cadmium could be preventing the normal peaking of ecdysteroids needed for molting. Since eyestalk-ablated crabs were used, a presumably direct effect of cadmium on Y-organ seems likely, by affecting cytoplasmatic calcium concentration and/or other actions.