||The soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18 mu M (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P < 0.05) the total number of protein spots (-41%, -52% and -60%, at 6, 12 or 18 M, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20-37% for lead; 36-50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP(+) reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29-34% for lead; 17-36% for zinc) (superoxide dismutase: SOD; proteasome alpha/beta subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase beta subunit (+16.3 fold after exposure to lead at 12 M). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems.