We employ Brillouin light scattering to measure the longitudinal modulus in supported thin polymer films in the direction normal to the film surface. In this first systematic experimental investigation, a reflection scattering geometry was utilized to probe elastic excitations localized between the free surface and the glass substrate, thus providing a direct access to the elastic constant along this direction. Thin supported polystyrene and poly(methyl methacrylate) Films with thickness in the range of 40 nm-3 mu m were explored. Comparison with the in-plane elastic constant obtained from the same optical technique but in transmission scattering geometry [Macromolecules 2007, 40, 7283] revealed no prominent directional tendency of the elastic properties with thickness. Nevertheless, there is now an experimental tool to address direction-dependent elastic constants in supported thin Films.