It is shown theoretically that a certain type of photophoresis, called gravito-photophoresis can contribute to the levitation of sunlit, absorbing particles in the middle atmosphere. Reasons are discussed why gravito-photophoresis appears far more effective for levitation than conventional longitudinal photophoresis: This type of force (a) remains related to the vertical direction regardless of the elevation of the sun; (b) it can have a lifting component; and (c) the force as a function of pressure exhibits a very broad plateau extending over a pressure range of nearly three orders of magnitude. The effect requires a restoring torque related to the vertical direction, induced by different action points of gravity and drag force, and a body-fixed photophoretic force, induced by a difference Delta alpha in accommodation coefficients alpha over the particle surface. Gravito-photophoretic levitation of a spherical model particle is investigated for the entire range of pressures. The model combines (1) the established mechanics of gravito-photophoresis, including perturbations of particle orientation by molecular collisions, with (2) the energy balance for a small light-absorbing particle irradiated by the sun, which exchanges heat with its surroundings by molecular transfer and thermal radiation, and (3) a recent formulation of the theory of Delta alpha-forces by Rohatschek (1995, J. Aerosol Sci. 26, 717). It is shown that at irradiances commensurate with the solar constant, levitation is restricted to a narrow particle radius range around 1 mu m. For those particles however, levitation appears possible over a broad pressure range corresponding to stratospheric and mesospheric altitudes.