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Adsorption of polydisperse colloid mixtures, including the limiting case of adsorption at surfaces precovered with smaller sized particles, was studied theoretically and experimentally. The theoretical analysis of these phenomena was carried out using the generalized random sequential adsorption (RSA) model suitable for irreversible systems. In order to determine the range of applicability of the RSA model for reversible systems, numerical simulations were compared with the analytical results stemming from the equilibrium scaled particle theory. Some theoretical predictions concerning adsorption at precovered surfaces and adsorption of bimodal mixtures were discussed, i.e., the blocking functions, the kinetics and the jamming coverages. These theoretical predictions were compared with experimental data obtained for model latex suspensions using the direct microscope observation method combined with the impinging jet technique. Adsorption kinetics at the mica surface precovered with smaller particles was studied as well as adsorption from bimodal mixtures of particles differing widely in size. The characteristic features of the RSA models were quantitatively confirmed in these experiments which supported the hypothesis that small colloid particles, polymer or surfactants present in trace amounts may significantly reduce adsorption rates of larger particles. [ABSTRACT FROM AUTHOR]