Disclosed are a method and a device for the biotechnological production of valuable products, in which a medium is fed to a bioreactor and is subjected to a fermentation process, the valuable product is gathered as a filtered permeate and/or concentrated retentate via a cross-flow filtration system that is mounted downstream thereof, and residues are once again fed to the bioreactor until being gathered as a retentate. Other materials can be fed to the bioreactor in a controlled manner in addition to the medium while the concentrated retentate and permeate can be gathered in a controlled manner. The fermentation process and the filtration process are regulated in a synchronized manner in an integrated system via a digital control unit.