We describe a new procedure for large-scale CB processing in the collection bag, thus minimizing the risk of CB contamination. A solution of 6% hydroxyethyl starch (HES) was added directly to the CB containing bag. After RBC sedimentation at 4 degrees C, the WBC-rich supernatant was collected in a satellite bag and centrifuged. After supernatant removal, the cell pellet was resuspended and the percent recovery of total WBC, CD34+ progenitor cells, CFU-GM and cobblestone area-forming cells (CAFC) evaluated. Results obtained with three different types of CB collection bags (300, 600 and 1000 ml) were analyzed and compared with those of an open system in 50 ml tubes. CB processing procedures in 300 and 1000 ml bags were associated with better WBC, CFU, CD34+ cell and CAFC recovery (83-93%). This novel CB processing procedure appears to be easy, effective and particularly suitable for large-scale banking under GMP conditions.