Abstract: The first results of isotopic investigations as a part of the hydrogeological study of northern Switzerland are presented. This study is part of the global geological research project of the NAGRA (National Co-operative for the Storage of Radioactive Waste) which is intended to provide the scientific knowledge required for the assessment of the feasibility of safe disposal of highly radioactive waste in the geological formations of the area. The aim of the hydrogeological research programme is to assess the natural conditions in the sedimentary sequence and the underlying granite basement, by regional investigation of hydraulic parameters, isotopic composition, and hydrogeochemistry at all existing wells (boreholes and natural thermal springs) and in 11 to 12 deep-drilled boreholes (to final depth of 1500–2500 m).