AbstractInline ultrafiltration (UF) can significantly increase the recoverable mass of biopharmaceutical products when pool tank volumes are limiting. Using relatively small commercially available ultrafiltration cassettes, a proof‐of‐concept study demonstrates that inline UF can significantly increase recoverable mass in an antibody purification process. With ever‐increasing cell culture titers pushing product masses to higher levels, inline UF offers a relatively easy‐to‐implement and less disruptive alternative to installing larger pool tanks and enables more cost‐effective production utilizing facilities designed for smaller bulk sizes. © 2010 American Institute of Chemical Engineers Biotechnol. Prog., 2010