Correlations between intermol. forces and ultrafiltration measurements for a thin polysulfone film and membranes modified for increased hydrophilicity by graft polymn. of 2-hydroxyethyl methacrylate and a model protein (hen egg-white lysozyme, Lz) suggest that altering either the chem. of the polymer surface or the soln. conditions should lead to a minimization of protein adhesion and hence fouling for a specific protein/polymer combination. Using the surface forces app., normalized adhesion forces were measured below, at and above the pI of Lz, and compared with corresponding permeation flux ratios from ultrafiltration expts. Simple exponential correlations were obtained relating the normalized adhesion forces to several different permeation flux ratios. Also, the amt. of protein adsorbed onto the membrane from soln. during filtration was linearly related to the adhesion force through the choice of soln. pH. The correlations imply that protein-polymer adhesive interactions are important during ultrafiltration. The results obtained for both a hydrophilic and a hydrophobic surface were compared. The hydrophilic surface exhibited lower contact angles, reduced adhesion forces, reduced adsorbed amt., and most importantly, reduced protein fouling. Long range attraction between adsorbed protein and hydrophobic polysulfone films was absent with the hydrophilic films. The results provide a fundamental mol. basis to the widely reported and obsd. phenomenon that hydrophilic membranes are known to foul less than hydrophobic ones during membrane filtration of protein solns.