Abstract: The invention is directed to a blood bag system for blood products comprising a bag (3) and at least one tubing (11) connected thereto, the system being made of at least partly transparent plastics material, wherein photoactive substances (31) may be enclosed in a closed-off section (A) of the tubing (11) of the ready-for-use system, which may be handled individually as an independent unit. Every blood bag system of this kind is adapted to be combined with another blood bag system, which may comprise one or several bags (3, 5, 7, 9) and may likewise be handled as an independent unit, by interconnecting both systems.