Bovine serum albumin and lysozyme mixtures of different mole fractions were adsorbed to colloidal alumina (116 nm) and titania particle (271 nm) suspensions of 2 vol % solid content for 16 h at pH 7.5. The total protein amount normalized to the powder surface area was 1000 ng/cm(2). The zeta potential of the protein-treated suspensions was measured as a function of pH and the isoelectric point (IEP) obtained. A simple prediction model in two refinement steps was derived and evaluated for the obtained IEPs. The best model fit which takes into account moles of protein and surface fractions yielded an average prediction error of 7.5% and a maximum error of 16.7%.