A radial flow packed-bed bioreactor was developed for continuous large scale culture of mammalian cells. A 5,000 ml-bed bioreactor (RA5000) was constructed to assess the scalability of this culture system. The medium feed rate and the glucose consumption rate attained 175 l/d and 450 g/d, respectively. The IL-6 production ina RA5000 corresponded to about 10 times that in a 400 ml-bed bioreactor (RA400).