Marine organisms have evolved a number of metabolic strategies to deal with potentially toxic trace metals. To determine how "detoxification" mechanisms such as metal-binding proteins and concretions are involved in the intracellular partitioning of trace metals in marine shellfish, the oyster, Crassostrea virginica, and the blue crab, Callincetes sapidus, were exposed to controlled levels of trace metals. Oysters accumulated cadmium readily and produced specific low molecular weight, cadmium-binding proteins. Blue crabs produced a single cadmium-binding protein in the hepatopancreas and gills when exposed to cadmium through food or water, respectively. Concretions appear to be of limited importance in detoxification.