Abstract: The invention relates to methods of improving protein production, e.g., large-scale commercial protein production, e.g., antibody production, utilizing a modified fed-batch cell culture method comprising a cell growth phase and a polypeptide production phase. The modified fed-batch cell culture method combines both cell culture perfusion and fed-batch methods to achieve higher titers of polypeptide products. Because the modified fed-batch cell culture method of the invention produces higher polypeptide product titers than fed-batch culture alone, it will substantially improve commercial-scale protein production. The invention also relates to a perfusion bioreactor apparatus comprising a fresh medium reservoir connected to a bioreactor by a feed pump, a recirculation loop connected to the bioreactor, wherein the recirculation loop comprises a filtration device, e.g., ultrafiltration or microfiltration, and a permeate pump connecting the filtration device to a permeate collection container.