Abstract: A process is provided for selectively removing protein aggregates from a protein solution in a normal flow (NFF) filtration process. Preferably, it relates to a process for selectively removing protein aggregates from a protein solution in a normal flow (NFF) filtration process and virus particles from a protein solution in a two-step filtration process. In a first step, a protein solution is filtered through one or more layers of adsorptive depth filters, charged or surface modified microporous membranes or a small bed of chromatography media in a normal flow filtration mode of operation, to produce a protein aggregate free stream. The aggregate free protein stream can then be filtered through one or more ultrafiltration membranes to retain virus particles at a retention level of at least 3 LRV and to allow passage therethrough of an aggregate free and virus free protein solution.