The study was performed to assess in vitro effects of reactive oxygen species (ROS, oxyradicals) on intracellular distribution of accumulated cadmium in digestive gland of the mussel Crenomytilus grayanus. In vitro induction of ROS (by Fe/ascorbate reaction) in tissue homogenates of Cd-accumulated mussels led to a significant increase in lipid peroxidation (as conjugated dienes and malondialdehyde) and also to decrease in reduced glutathione and Cd-binding protein contents. Also fraction of MT-like proteins (20-22 kDa) has been shifted to a higher molecular weight area (40-45 kDa), which indicates dimerization of the protein. The level of intracellular vesicle-stored cadmium (within membrane compartments like lysosomes) was decreased significantly in oxyradicals-exposed tissue crude homogenate of mussels in comparison with controls. Additionally, Cd distribution among three weight classes of cytosol proteins has been significantly changed after ROS exposure. Taken together the results, there is a clear indication that ROS induce an oxidative stress resulting in damaging of intracellular Cd-binding compartments that may trigger (or contribute) the toxicity of this metal. Thus, from our experimental results and reviewed information follows that under high "pressure" of heavy metals on marine environment the aquatic organisms can show higher sensitivity to normal variations of natural factors of the environment or even decrease the range of tolerance to their variations.