OB stars are very active actors shaping their environment and contributing to the chemical and dynamical evolution of their host galaxies. Accurate analyses of massive stars are thus a key ingredient in our interpretation of the light coming from the Milky Way and nearby galaxies. These analyses rely in the use of state-of-the-art model atmospheres, that have to be as realistic as possible. In our project, we aim at testing the self-consistency of our model atmospheres when carrying out simultaneous analyses in the optical and the near IR. This is particularly relevant for our Galaxy, where extinction obscures the optical wavelengths and the inner OB population can only be studied in the IR. We compare the behaviour of H and He lines in both wavelength ranges and their potential as stellar parameters diagnostics. We determine stellar parameters for a sample of OB stars covering a range of spectral types and luminosity classes and compare the results obtained in the different wavelength ranges.