The phenomenon of euperlattice formation on an adeorbed layer is investigated by using both Kirkwood's theory and Bøthe's therry of ørder-disorder transformation. Jt is shown that when the interaction energy betweeu the adsorbed atoms is positive and when the temperature is below a certain eritical temperature the,slope of the adsorption igothermals and the heat of orption have a diseontinuity a a certain transition θ, where θ is the iraction of the surface covered by adsorbed atoms. This transition θ is situated symmetrically about the value θ=1/2, suoh that if θt is the transition θ, ther 1-θt is also one. When θ <θt and θ> 1-θt no superlattice is formed.