Interstadial and interglacial deposits including peat layers are widespread in Northern Europe and enable us to reconstruct the past climate and vegetation history. Such reconstructions require a reliable and precise chronological framework. Uranium series dating, sedimentological and palynological investigations were performed on a peat deposit at Wedel in Schleswig-Holstein. Previous palynological studies suggested a Middle Pleistocene age for these interglacial deposits. The sediment sequence including a fen peat of 130 cm thickness at a depth of 14-15 m below surface was drilled and cored. Palynological results correlate well to the late Holsteinian Interglacial, but the radiometric age determination failed due to U-series open system behaviour. Comparison of results obtained at Wedel with those from Holsteinian Interglacial deposits in Northern Germany reveals the weakness of numerical age determinations. Furthermore, a brief discussion on radiometric data available of the Middle Pleistocene Reinsdorf Interglacial peat deposits at Schöningen is given, as the laboratory has performed further quality assurance processes. A spike calibration led to new calculations on isotope activities, resulting in higher values shifted by 5-7 % and corrections on published data of the same order. The age of the Reinsdorf Interglacial peat deposit 13 II-2c5 cannot be maintained as the assigned errors inhibit the calculation of reasonable mean ages nearby the methodological age limits.