[en] Full text: In evaluating groundwater resources, it is fundamental to define a precisely delimited spatial framework. This framework which represents the aquifer, is defined by its geometry, its internal characteristics, its boundary conditions and its dynamics. These informations are difficult to acquire by conventional methods (drilling, geophysics) essentially due to economical resources (G. Castany et al. 1976). The understanding of groundwater flow in large scale African sedimentary basin is confronted to the absence of reliable piezometric data. Yet this knowledge is necessary for better management of groundwater resources. The lack of data is largely due to the poor quality of topographic levelling. The only topographic maps used for drawing piezometric contours are of a 1/200000 scale with elevation contours of 40 meters. Such precisions do not allow the characterization of flow on a large scale (> 1 deg. square) in the case of vast transboundary basins (Dakoure et al., 2002). The Taoudeni sedimentary basin is an example of this type of aquifer in the southwestern Burkina Faso and the southern Mali. The isotopic studies provides independent informations whose interpretations, combined with hydrogeological models, can contribute to the knowledge of: the structure of the aquifer system (mono or multi layer); the type of recharge and renewal of the reserves; boundary conditions. Carbon-14 measurements which allow determination of water residence time, can be used to calculate the Darcy velocity when the effective porosities are known. Isotopic investigations were undertaken in the two countries. The measurements available permit a detailed interpretation of the groundwater behaviour in a large scale. (author)