Abstract 1. Sea mussels, Mytilus edulis, were exposed to cadmium chloride at 0–500 μg Cd/l for 48 hr. The gills were excised and incubated with protein and RNA precursors. The exposure resulted in a concentration-dependent inhibition of the synthesis of proteins and of RNA. The inhibitory effect was most pronounced in RNA synthesis. 2. RNA was extracted from the gills as total RNA or as polyadenylated RNA. The translational activity of RNAs and the induction of mRNA for metallothionein-like proteins were studied by translation in a cell-free system. 3. Exposure of the animals to cadmium at 500 μg/l caused a 5-fold increase in proto-oncogene c- fos mRNA.