AbstractA flat‐bed hollow‐fiber cell culture system has been developed which maximizes the utilization of the large fiber surface while diminishing significantly the problems inherent in a cartridge‐type reactor. The reactor core consists of a shallow bed of hollow fibers sandwiched between two stainless‐steel microporous filter plates through which the media flow is directed normal to the plane of the fiber bed. Reactors with both 930 and 9300 cm2of fiber surface have been successfully constructed and operated. A variety of cells has been grown in these reactors including SV3T3 cells, baby hamster kidney cells, Vero cells, and rhesus money kidney cells, and cell products such as plasminogen activator and migration inhibition factor (MIF) were produced. This system offers an excellent prototype for scaleup