Membrane surface characteristics effect on adsorptive fouling and the consequences of such fouling were studied. Results showed that different membrane characteristics caused significantly different behavior with respect to polysaccharide fouling. Membrane chem. (polyethersulfone vs. cellulosic) had the dominant effect, but av. pore diam. of the membrane skin layer in relation to the av. size of dextran was also important (for polyethersulfone). For the same solute size, the extent of protein fouling was larger than dextran fouling.