Résumé : Magnesium promotes endothelial migration, an event which is orchestrated by a complex interplay between protein tyrosine kinases and phosphatases. We found that high extracellular concentrations of magnesium do not modulate the levels and the activation of FAK and Src, two tyrosine kinases involved in driving cell migration. Interestingly, we show that magnesium induced-endothelial motility correlates with the downregulation of HD-PTP, a potential tyrosine phopshatase previously shown to be involved in modulating cell migration. The decreased amounts of HD-PTP are not dependent upon transcriptional mechanisms. In contrast to Fibroblast Growth Factor-induced HD-PTP downregulation, the proteasome seems not to be involved in regulating HD-PTP levels in endothelial cells cultured in high magnesium containing medium. Our results indicate that, in the presence of high magnesium concentrations, endothelial cells are stimulated to migrate through complex mechanisms involving also HD-PTP.