A Combined Electrolysis Catalytic Exchange (CECE) facility is running at the Tritium Laboratory Karlsruhe (TLK) in order to investigate the simultaneous transfer of tritium and deuterium between various molecular hydrogen isotopes in gas and water, employing a Liquid Phase Catalytic Exchange (LPCE) column. Currently a glass column with an active height of 2 m and a diameter of 58 mm is being used. Experiments are performed to determine the height equivalent of theoretical plate (HETP) and the mass transfer coefficients during simultaneous deuterium and tritium exchange between deuteriated and tritiated water and gaseous hydrogen isotopes. The experiments are aimed to provide the data required for the design of large isotopic exchange columns needed for the recovery of tritium from waste water generated during the operation of the tritium facilities of fusion machines. The exchange column is filled with a mixture of catalyst (platinum on charcoal and PTFE) and ordered packing layered in the column. Pre-heated water at the working temperature is fed into the column from the top and tritium-deuterium-hydrogen mixtures saturated with wa ... mehrter vapour from the bottom. Hydrogen depleted of deuterium and tritium is removed from the top of the column. The column has several extraction points for both liquid and gas phases for analysing their compositions. Deuterium and tritium distribution along the column will provide information about possible differences in the HETP along the column and the differences in the mass transfer coefficients. The measured concentration values will also be used for comparison with the predicted values from the mathematical model, which thereby will be validated and improved. For safety reasons related to the tritium inventory of tritiated water, a solid polymer type electrolyser is used in the experimental facility. In addition no stripper for e.g. K OH need to be considered when such an electrolyser is used. The experiments allowed to determine the enrichment factor between gas and liquid for both deuterium and tritium. Preliminary tests used a Vapour Phase Catalytic Exchange (VPCE) system instead of an electrolyser to prepare the required composition of hydrogen-deuterium-tritium. The isotopic compositions of the liquid phases are analysed with an on-line infrared spectrometer and a liquid scintillation counter. For the gas phase, a Quadrupole and an Omegatron mass spectrometer as well as a proportional counter are employed. The model, the experimental results, the HETP and also the gas/vapour mass transfer coefficients for deuterium and tritium are presented.