Viral filtration (VF) of concentrated monoclonal antibody (MAb) solutions (> 4 g/L) has the potential to improve downstream purification processes by eliminating VF feed stream dilution and by reducing filter area with a concomitant reduction in filter costs. Evaluation of hollow fiber membrane filters was performed with MAb solutions ranging in concentration from 4 to 20 g/L. The resulting flux profiles were fairly constant with values between 45-65 LMH, even when filter loading was extended to 200 L/m². In contrast, other types of viral filter, such as PVDF disc membranes, were plugged by MAb solutions with concentration > 4 g/L well before 50 L/m². Viral clearance data confirm the ability of high-capacity hollow fiber membranes to achieve > 3 log reduction of two different model viruses (XMuLV and MMV), independent of MAb concentration. Finally, the scale-up properties of different viral filters will be discussed in relation to a theoretical model.