Time-dependent X-ray microscopy has been applied for the first time to follow an electrodeposition process : that of copper on a glassy carbon electrode. From a series of X-ray microradiographs taken every 20 s it is possible not only to measure directly the increasing thickness of the coating but also to evaluate the copper sulfate concentration profile in the electrolyte at the corresponding instants of acquisition. When the electrodeposition conditions lead to ramified growth close to coating/electrolyte interface, local variations of the ionic concentration are observed as a function of time and of coordinates. The lateral resolution is in the 10-20 mu m range and relative concentration changes of few percent are easily detected.