A blood processing system comprising a separation device, a first processing device and a second processing device, which system is embodied in a blood processing apparatus and a disposable fluid circuit wherein the disposable fluid circuit comprises a first, second, third and fourth pathway, and a separation chamber; wherein the separation device is configured to separate the blood into two or more components, the first component being substantially cell-free plasma and the second component containing cellular components, wherein the first processing device comprises a container access device suitable for connection to a container comprising a plasma replacement fluid; wherein the second processing device comprises a retention container for at least one separated cellular component and a container access device suitable for connection to a container comprising donated cellular components or replacement fluid, wherein the processing apparatus comprises a controller, the separation device and at least one cassette (16, 16a, 16b) with a series of valves and one or more pumps, wherein the separation device and the cassette are configured for mounting the disposable fluid circuit to enable processing of the blood and/or blood components applied into the disposable fluid circuit, wherein the controller is configured for control of: receiving in the first pathway blood drawn from a blood source, the first pathway leading to the separation chamber mounted to the separation device; receiving in the second pathway a first component from the separation chamber, the second pathway transporting at least a portion of the first component to the first processing device, said first component being a plasma component, altering the first component in the first processing device in at least one of volume, constitution, and composition, to produce a first output; receiving in the third pathway the second component from the separation chamber, the third pathway transporting at least a portion of the second component to the second processing device, altering the second component in the second processing device in at least one of volume, constitution, and composition, to produce a second output, and receiving in the fourth pathway the first output and the second output for combining them into treated blood, particularly treated whole blood, and transporting it to a blood access device or to a storage container, wherein the controller is further configured for control of a ratio of exchanged plasma and exchanged red cells. receiving in the first pathway blood drawn from a blood source, the first pathway leading to the separation chamber mounted to the separation device; receiving in the second pathway a first component from the separation chamber, the second pathway transporting at least a portion of the first component to the first processing device, said first component being a plasma component, altering the first component in the first processing device in at least one of volume, constitution, and composition, to produce a first output; receiving in the third pathway the second component from the separation chamber, the third pathway transporting at least a portion of the second component to the second processing device, altering the second component in the second processing device in at least one of volume, constitution, and composition, to produce a second output, and receiving in the fourth pathway the first output and the second output for combining them into treated blood, particularly treated whole blood, and transporting it to a blood access device or to a storage container, wherein the controller is further configured for control of a ratio of exchanged plasma and exchanged red cells.