The effects of solution chemistry on the rate and extent of adsorption of a protein (BSA) and humic acid (Suwannee River humic acid) onto a regenerated cellulose ultrafiltration membrane were studied. Isotherms were performed to determine equilibrium adsorption behavior. Rate of adsorption was determined by measuring adsorbed mass as a function of time. Experiments were performed at differing conditions of pH, ionic strength and bulk feed concentration. For both compounds, adsorption was higher at lower pH values. Adsorption decreased as pH increased. Increased salt concentration reduces electrostatic repulsion between like-charged material (increasing adsorption) and decreases electrostatic attraction between oppositely charged material (decreasing adsorption), These interactions between the adsorbing material and the membrane surface affect the adsorption rate, which was evaluated using two mechanistic models, The modeling was designed to determine the governing mechanism in adsorption onto the hydrophilic membrane surface. These models confirmed that, under conditions of this study, the transport rate to the membrane surface is fast compared to the reactions at the membrane surface, thus electrostatic interactions are very important in determining adsorption of this material onto the membrane. Controlling electrostatic interactions could reduce adsorption of protein and humic material onto the membrane, consequently reducing long-term membrane fouling. Parameters from the models developed in this study can be used to determine the "fouling potential" of a given feed stream, (C)2000 Elsevier Science B.V. All rights reserved.