One of the primary problems in membrane-based protein separation is membrane fouling. In this study we explored the feasibility of employing Rayleigh light scattering data from fluorescence studies combined with chemometric techniques to determine whether a correlation could be established with membrane fouling phenomena. Membrane flux was measured in a dead-end UP filtration system and the effect of protein solution properties on the flux decline was systematically investigated. A variety of proteins were used as a test case in this study. In parallel, the colloidal behavior of the protein solutions was assessed by employing multi-wavelength Rayleigh scattering measurements. To assess the usefulness of Rayleigh scattering measurements for probing the colloidal behavior of proteins, a protein solution of beta-lactoglobulin was used as a base-case scenario. The colloidal behavior of different beta-lactoglobulin solutions was inferred based on published data for this protein, under identical solution conditions, where techniques other than Rayleigh scattering had been used. Using this approach, good agreement was observed between scattering data and the colloidal behavior of this protein. To test the hypothesis that a high degree of aggregation will lead to increased membrane fouling, filtration data was used to find whether the Rayleigh scattering intensity correlated with permeate flux changes. It was found that for protein solutions which were stable and did not aggregate, fouling was reduced and these solutions exhibited reduced Rayleigh scattering. When the aggregation behavior of the solution was favored, significant flux declines occurred and were highly correlated with increased Rayleigh scattering. (C) 2010 American Institute of Chemical Engineers Biotechnol. Prog., 26: 772-780, 2010