Improvements in upstream process development often generate complex, high titer process streams, placing considerable demands on downstream processing steps. Protein aggregates in these feeds influence hydraulic performance of virus filters resulting in over-sized platforms and a significant impact on process economics. Virus filters from a broad range of manufactures provide robust viral clearance but the impact of aggregates on flux is dependent on the filter. The impact of conditioning protein solutions using prefiltration was assessed with several monoclonal antibody feed streams. Adsorptive depth or surface modified membrane prefilters upstream of the virus filter were shown to remove foulants from protein solutions, enhancing performance of the virus filter.