We propose to do spectrophotometry using ISOPHOT covering the 2- 12 micron range of a selection of M dwarfs, which are also GTO program targets for photometric observations extending to much longer wavelengths. The goal is to determine the temperature stratification, effective temperature, bolometric luminosity and the general atmospheric structure of low mass stars using a more sensitive and accurate approach than studies at shorter wavelengths. We hope also to study how the atmospheric structure depends both on effective temperature (mass) and on the degree of chromospheric/coronal activity. The temperature stratification especially high in M dwarf atmospheres is complicated and uncertain mainly because there is probably only a very thin outer radiative zone, which sets the boundary for the adiabatic convection zone extending to the center of the star. The effective temperature of the star is also sensitive to this boundary. Our main purpose is to determine the depth of the radiative layer, and how this depends on stellar parameters and surface activity. In the ISO spectral region, the continuum is generally formed high in the physical atmosphere and is therefore sampling the critical temperature range. The main reason for this is the dominance of the H-minus free-free opacity; it increases by nearly two orders of magnitude over the 2-12 micron range. Optical and near-IR wavelength studies, on the other hand, are complicated by the dominance of much more uncertain and complex molecular and atomic bands.