Uranium is a naturally abundant element which has been used in several industries. Internal exposure could occur via three main pathways that are ingestion, inhalation and wounds. It has been recently shown that chronic ingestion of uranium in drinking water induces an important uranium accumulation in kidney with a perturbation of iron metabolism in this organ. Whereas uranium speciation is a key parameter to elucidate the chemical reactivity and the mobility of an element, it remains poorly documented in most of environmental and biological media. A few examples of uranium complexation with biomolecules have been published recently but most of them are in vitro studies whereas in vivo experiments remain poorly investigated. In order to better understand possible competition of uranium towards metals involved in the metal-protein binding, i.e. iron, copper, calcium, a study on uranium speciation was investigated by doing an in vivo screening of target proteins likely to bind it in kidneys of exposed rats. Rats were chronically exposed via contaminated drinking water at 40mgL~' and killed 9 months after the beginning of exposure. Kidneys were dissected out and protein extract was prepared. Then, separation of renal proteins by isoelectric focusing gel electrophoresis (IEF) and two-dimensional gel electrophoresis (2-DE) followed by LA-ICPMS analysis were performed. IEF-LA-ICP MS showed that uranium could specifically bind few proteins in kidney whereas 2-DE-LA-ICP MS could indicate that uranium is not covalently bound to proteins in this organ. The results suggested that even at moderate concentrations of exposure, uranium can be observed chelated with some renal proteins that is very encouraging to understand the entry, storage and elimination of this element in kidneys. © by Oldenbourg Wissenschaftsverlag, Munchen.