A model investigation is presented, showing the effects of the topography of heterogeneous solid surfaces on adsorption from binary liquid mixtures onto solid surfaces. Equations are developed for excess adsorption isotherms and heats of immersion, for both patchwise and random surface topography, when the adsorbed solution is a quadratic mixture. Using these equations, numerical model calculations are carried out for some typical values of heterogeneity and interaction parameters. -- AATA