While continuous (perfusion) culture of mammalian cells might reduce the reactor size owing to the high cell density, there is the problem of higher medium cost; however, this problem is expected to be solved by the reuse of growth-promoting components in the culture supernatant. The polymer fraction (PF, 10 kDa-220 nm) collected from the supernatant of serum-free repeated-batch culture of Chinese hamster ovary (CHO) cells in not only adhesion but also suspension promoted the cell growth in respective serum-free cultures. PF contained CD81-positive exosomes and proteins, both of which were necessary for its growth-promoting activity. Consequently, the medium cost for the continuous (perfusion) serum-free suspension culture of CHO cells may be decreased by the repeated collection and addition of PF that contains exosomes and growth factor proteins. (C) 2020, The Society for Biotechnology, Japan. All rights reserved.