A single-use fluid circuit for recovering leukocytes in conjunction with separation of biological fluid into two or more components, comprising: a separator having an inlet for receiving the biological fluid, a first outlet for a separated first component, and a second outlet for a separated second component; a leukocyte reduction filter having an inlet and an outlet ; a first fluid flow path in fluid communication with the inlet of the separator and configured to be connected to a source of biological fluid; a second fluid flow path connecting the first outlet of the separator to the inlet of the leukocyte reduction filter ; a first collection container for receiving leukocyte-reduced first component; a third fluid flow path connecting the outlet of the leukocyte reduction filter to the first collection container ; a source of additive solution; a fourth fluid flow path between the first fluid flow path and the source of additive solution ; wherein the fluid circuit further comprises: a fifth fluid flow path between the source of additive solution and the second fluid flow path leading to the leukocyte filter ; a source of eluate ; a sixth fluid flow path between the source of eluate and the third fluid flow path , so as to permit eluate to flow to the outlet of the leukocyte filter to backwash the filter ; a second collection container for receipt of recovered leukocytes, and a seventh fluid flow path between the second collection container and the fifth fluid flow path , so as to permit the recovered leukocytes and eluate to flow out of the inlet of the leukocyte filter and sequentially through the second fluid flow path , the fifth fluid flow path and the seventh fluid flow path and into the second collection container . a separator having an inlet for receiving the biological fluid, a first outlet for a separated first component, and a second outlet for a separated second component; a leukocyte reduction filter having an inlet and an outlet ; a first fluid flow path in fluid communication with the inlet of the separator and configured to be connected to a source of biological fluid; a second fluid flow path connecting the first outlet of the separator to the inlet of the leukocyte reduction filter ; a first collection container for receiving leukocyte-reduced first component; a third fluid flow path connecting the outlet of the leukocyte reduction filter to the first collection container ; a source of additive solution; a fourth fluid flow path between the first fluid flow path and the source of additive solution ; a fifth fluid flow path between the source of additive solution and the second fluid flow path leading to the leukocyte filter ; a source of eluate ; a sixth fluid flow path between the source of eluate and the third fluid flow path , so as to permit eluate to flow to the outlet of the leukocyte filter to backwash the filter ; a second collection container for receipt of recovered leukocytes, and a seventh fluid flow path between the second collection container and the fifth fluid flow path , so as to permit the recovered leukocytes and eluate to flow out of the inlet of the leukocyte filter and sequentially through the second fluid flow path , the fifth fluid flow path and the seventh fluid flow path and into the second collection container . <EOS>