In this contribution we give a progress report for our work intending to approach in a more complete way the problem of a quantitative calibration of the Mg2 index (Faber et al. 1977, A.J., 82, 941; Buzzoni, Gariboldi & Mantegazza 1991 submitted to A.J.). We have first investigated empirically the relationship between the index and the fundamental parameters for a wide set of Galactic standard stars deriving a detailed calibration for dwarfs and giants. This allowed to build up synthetic models for stellar populations exploring Mg2 in the galaxies with varying overall distinctive parameters of the populations.