An experimental device able to determine the moisture content. of wood using X-ray attenuation is used to study the imbibition of beech samples (Fagus silvatica). The apparatus includes an X-ray generator, a protective tube, collimating plates and a 50 mm detector. Detected particles can be categorised by energy (accuracy, of the order of 20 %) or by position (accuracy 100 mum). The independent choice of both the energy spectrum (through the voltage) and the counting rate (through the current intensity) makes the installation very flexible. However, a rigorous treatment is necessary to deal with the attenuation of a polychromatic spectrum. The appropriate calculations are presented and validated with homogeneous samples made of wood and water. In addition, some results are presented with samples heterogeneous in density and moisture content. Finally, the experimental device is used to study the evolution of moisture content during saturation experiments, for which the moisture migration is mainly due to capillary forces. The geometrical configuration was so arranged that the transfer can be studied in - two directions simultaneously.