Deposition, retention and in-depth penetration of deuterium was investigated in carbon fibre composites (CFC). Comparative studies were also performed for isotropic graphite and carbon-silicon (5 or 20% Si) composites. The materials were exposed to fluxes of deuterium in a hollow cathode device and in the TEXTOR tokamak. The irradiated targets were studied by a number of techniques in order to characterize their surface composition and structure. Nuclear reaction analysis, Rutherford backscattering spectroscopy, laser profilometry, crystallographic as well as microscopic methods were applied, and thermally and ion induced release were studied. The studies performed in several time steps revealed a systematic decrease of the deuterium content in the near surface layer (1.5 μm thick) of CFC substrates exposed to the hollow cathode plasma: from 6.8×10¹⁸ cm^-2 to 4.18×10¹⁸ cm^-2 and 3.76×10¹⁸ cm^-2 after 1, 81 and 112 days following the exposure, respectively. Moreover, in these samples a pronounced content of deuterium, even 60 times higher than the background level, was found beneath the exposed surface indicating deep penetration of D atoms through the layered structure of CFC. Thermally stimulated desorption at 1100°C resulted in the release of more than 99.9% of D atoms from the substrate. The disappearance of deuterium was accompanied by topographical changes of the surface layer as observed by scanning electron microscopy.