['Microbial contamination of peripheral blood progenitor cell components (PBPCs) may cause severe complications in immunosuppressed recipients. Therefore, principles of Good Manufacturing Practice (GMP) are applicable for processing of PBPC components to reduce potential risks of contamination.', 'It was investigated in a retrospective study whether the microbial contamination of PBPC components could be reduced after processing in improved clean areas according to the "Manufacture of Sterile Medicinal Products." Starting in 1994, a total of 1478 autologous and allogeneic PBPC components have been collected and processed into 3149 cryopreservation bags at the Department of Transfusion Medicine. Sterility testing was performed for all bags. Until December 1998, 783 PBPC components were processed at a clean bench only (group I). Thereafter, 695 PBPC components have been processed at a clean bench located in a clean area with an airlock system for personnel and equipment (group II).', 'In group I, 16 of 1555 bags (1.03%) showed positive results in the first sterility testing. In group II, 21 of 1594 bags (1.32%) were positive (p = NS). The clinical follow-up was inconspicuous.'] Does processing of peripheral blood progenitor cell components in improved clean areas reduce the rate of microbial contamination?