The objective of this study was to examine how membranes irreversibly foul with organic matter, by characterizing the interaction between the nanofiltration (NF) and ultrafiltration (UF) membranes with proteins, polysaccharides (PSs) and polyhydroxyaromatics (PHAs) using a variety of analytical techniques. The membranes used in these experiments were Spectrum (R) Molecular/Por(R) NF and a UF cellulose ester membrane. The MWCOs were 100 and 100,000 Da respectively. Model PHA, PS and protein molecules (rosolic acid, polygalacturonic acid and bovine serum albumin respectively) were used to simulate fouling by the various components of dissolved organic matter (DOM) in surface waters. The feed concentrations used in these experiments are 1000 mg/L, 100 mg/L and 29 mg/L respectively. The lower dosing with PgA and RA was due to solubility constraints. To foul the membranes, bench-scale dead-end filtration was used to simulate membrane filtration of the NOM-surrogate organic molecules. Clean water flux tests were run prior to and after the fouling filtration cycle. Includes 3 references, figures.