Membrane morphology is compared to protein deposition under passive adsorption and ultrafiltration conditions. Solute resistance of protein deposits for membranes of varying roughness, structure, and permeability can vary dramatically with operating conditions. Using Brunauer-Emmett-Teller adsorption isotherm (BET), study of the internal area and accessibility of several ultrafiltration membranes to protein deposition allows better understanding of the fouling mechanisms and interpretation of adsorbed protein quantities.