We show our very first results regarding the stellar atmospheric parameter determinations (Teff, log g, [M/H]) of M-type stars observed with CARMENES by means of the spectral synthesis method. We have selected spectral ranges around iron and titanium lines and molecular bands in three reference M-type stars: GX And (M1.0 V), Luyten's star (M3.5 V), and Teegarden's star (M7.0 V). We employ PHOENIX stellar model atmospheres, the radiative transfer code Turbospectrum and line data from the VALD3 database to obtain a grid of synthetic spectra, and a Markov Chain Monte Carlo process implemented in SteParSyn code to derive the value of the stellar atmospheric parameters.

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