Abstract: The present disclosure provides high viscosity ultrafiltration/diafiltration (UF/DF) and single-pass tangential flow filtration (SPTFF) processes used in the purification of polypeptides. A method for purifying a polypeptide from a polypeptide preparation may include the following steps in order: a) subjecting the polypeptide preparation to one or more purification processes and recovering a first resulting pool having a viscosity of about 5-40 cP; and b) subjecting the pool recovered from step a) to a SPTFF operation comprising use of membranes in either or both a serial membrane and/or a parallel membrane configuration and recovering a second resulting pool having an operating viscosity of about 41-400 cP, wherein, i) the operating temperature is about 15-55° C., and ii) the feed flux is about 5-50 L/m2/hr (LMH).