The present invention pertains to a system for culturing cells comprising a culturing bag and a continuous flow centrifuge wherein the cells are continuously separated from the supernatant and are recycled into the culturing bag. Further provided are methods for culturing cells and for producing a biological substance using the device for culturing cells, and the use of a bag for culturing cells in said device or said methods. In particular, a perfusion system for culturing cells is provided wherein the wave technology for culturing cells is combined with continuous flow centrifugation for separating the medium from the cells.
