Cellular toxicity of cadmium was studied in gill tissue of the sea mussel, Mytilus edulis. Mussels were exposed to cadmium chloride at 50 or 250 μ,g Cd/L for short periods. Then the gills were excised and incubated with [35S]-methionine or cysteine for 4 hr. Uptake of radiolabeled amino acids by the isolated gills was not affected by cadmium, whereas the incorporation of label was significantly decreased after Cd exposure. Two dimensional gel electrophoresis was used to analyze the de novo synthesized gill proteins. It revealed that the expression of particular proteins was differentially altered by cadmium. One dimensional gel analysis by [35S]-cysteine labeled gill proteins demonstrated that cadmium induced, in a concentration-dependent manner, a cysteine-rich protein with a molecular weight of approximately 13 kDa, consisting of two isomers with low isoelectric points.