Temperature and species mole fraction profiles have been measured in laminar premixed H-heptane/02/Ar and iso-octane/02/Ar flames. Both flames have been stabilized on a flat-flame burner at low pressure (6.0 kPa), and species identification and concentration measurement have been performed by mass spectrometric analyses of samples withdrawn locally by molecular beam formation. Temperature profiles were measured by Pt - Pt 10% Rh thermocouples with corrections of the signals to compensate radiative heat losses. A wide range of equivalence ratios extending to 0.7 up to 2.0 has been considered in order to check how the nature of the fuel influences the evolution with this parameter of the species mole fraction profiles