Embrittlement of high-strength steel is known to be caused by hydrogen penetration into the network of the metal. However, the penetration mechanism of hydrogen into the steel is still under discussion, as it is not so easy to detect and measure the hydrogen in steels. In this paper, relatively large commercial cold drawn pearlitic steel wires have been submitted to stress corrosion cracking under different environments. After these tests, Nuclear Resonance Reaction Analysis, NRRA, has been used to detect the presence of the hydrogen and its quantity, which has confirmed the presence of H in the case of brittle fracture. In addition, once the presence of hydrogen has been confirmed, the penetration of the hydrogen into the unit cell of the ferrite has been deduced from the analysis of the steels by neutron diffraction, from the shift of the d-spacing after the experiments. The application of NRRA and Neutron Diffraction techniques have been shown as very promising techniques to study the mechanisms of the embrittlement of the steel to the hydrogen present in the metallic lattice.