The adsorption of proteins to membrane surfaces can lead to the reduction of a permeate flux and represents a serious impediment to efficient membrane filtration operations. The factors influencing protein adsorption, permeate flux and overall membrane fouling during cross-flow filtration of whey protein solutions using 50 nm pore size ultrafiltration zirconia membrane and 200 nm pore size microfiltration alumina membrane were examined in this study. The permeate flux was observed to be a function of protein concentration and transmembrane pressure and followed classic membrane filtration behavior for the membranes studied. Studies of the fouling resistances, coupled with static adsorption studies, indicated that adsorption-related pore plugging plays a significant role in the larger pore alumina microfiltration membranes.