In order to investigate the importance of NLTE effects on the models presented in this paper, we have calculated small number of representative NLTE models with parameters roughly appropriate for the Sun and Vega ( Lyr). We include a large number of levels and lines in NLTE in order to make the model calculations as realistic as possible. In addition, species that we do not include explicitly in NLTE are included in the LTE approximation in order to describe their effects on the model structure and the spectrum, see [Hauschildt et al.(1997b)Hauschildt, Allard, Alexander, and Baron] and [Aufdenberg et al.(1997a)Aufdenberg, Hauschildt, Shore, and Baron] and references therein for details of the method. This allows us to determine which models require NLTE and for which models LTE provides an adequate description of line formation. In the outer, optically thin, regions of the atmosphere, NLTE effects will always become important (even in the absence of a chromospheric temperature rise), but for models of stellar photospheres, it is crucial to know if NLTE effects are important in the line forming regions. We have computed detailed NLTE models for two cases: for relatively cool, G-type stars we chose model parameters approximately appropriate for the Sun; and for hotter stars, where we chose model parameters appropriate for Vega. The models serve to demonstrate the effects of NLTE on the structure and spectra, we did not make any attempt to produce detailed fits to either the Sun or Vega. The models include a large number of NLTE species and use the same version of PHOENIX and the same input physics as the NextGen models.