[en] We discuss the permeation of hydrogen through metals and alloys such as iron, nickel, steels and Inconel wherein H dissolves endothermically from an H₂ gas. We assume first that trapping centers, surface contamination layers, the saturation of the H surface coverage and the implantation profile - when energetic ions drive the permeation - can be neglected, that a quasi-equilibrium exists between the H atom concentration ν in the adsorbed layer and c in the near surface layers and that the H solubility and diffusivity are homogeneous in the membrane. We evaluate thereafter separately the influence of these various effects and identify the parameter domains where appreciable corrections result. The permeation phenomenon is complex even when these simplifications are made: the penetration rate is proportional to the flux of thermal molecules, atoms or energetic ions - depending upon the case - which strike the surface; the diffusion in the metal is proportional to the gradient of c; the release rate depends on c²; the time-dependent diffusion equation includes a double spatial derivative of c. Permeation can only be fully described when computer codes such as PERI is used. Simple analytical relations are however obtained in several limiting cases. They are the object of this report. Some of them had already been derived by other authors but they were not shown to be part of a single, self consistent permeation model. A comparison of predicted and experimental results shows that the simplified model describes surprisingly accurately the hydrogen exchange between gas and metal solutions. (orig./GSCH)