In order to investigate the effects of irradiation on the spectra of the cooler components of Algol binaries, a modified version of the Upsalla Model Atmosphere code (U.M.A.) has been used. The upper boundary condition was changed to take into account the external radiation field and an automatic procedure to prevent numerical oscillations was introduced. In order to simulate the external flux from the hot component we have used the Kurucz grid interpolated for the wavelenghts adopted in U.M.A. code. Since secondary stars of Algoltype binaries normally have deep convective layers, we impose the condition that the entropy of these zones must be the same in the irradiated and in the non-irradiated models.