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It is reported that annealing and deformation experiments at 800°C and 650°C in a H 2 gas atmosphere change the plastic -, electrical - and paramagnetic properties of deformed silicon. Effusion experiments prove that hydrogen can be introduced by the used annealing/deformation procedures into the bulk of Si if dislocations are present. In particular, the annealing of Si at 800°C in a H 2 gas ambient leads to an activation of surface sources for the introduction of dislocations during the deformation and the stress exponent m for dislocation motion is reduced. In addition it is shown that the deformation induced ESR-defect spectrum can be reduced by exposure of the crystals to molecular hydrogen in a rather similar but more efficient way than it can be done by exposure of the crystals to an atomic hydrogen plasma at low temperature. From this similarity and from a H 2 induced reduction of the specific resistance we consider it most likely that passivation of deep defects was achieved by exposure of the crystals to the H 2 gas ambient but it cannot be excluded that the H 2 treatments just changed the defect formation rate. In order to observe such effects, a critical temperature T c in the range of 650°C c ≤ 800°C needs to be overcome and this indicates the presence of an activation barrier against incorporation of hydrogen into Si from the H 2 gas ambient.