The aim of this study was to investigate the cryobiological characteristics of placental cord blood (PCB) cryopereserved by using BioArchive auto-preserved liquid nitrogen system (BioArchive system). After Hespan depletion of red blood cells, 5 ml mixture of DMSO and 10% Dextran 40 were added into 20 ml of enriched leukocyte. 53 PCB units were cryopreserved as following protocol: pre-freeze rate 10 degrees C/min, start freeze temperature -3 degrees C, end freeze temperature -10 degrees C to -15 degrees C, post freeze rate 2 degrees C/min, and end temperature -50 degrees C. After rapid thawing at 38 degrees C, the PCB were washed with 5% human serum albumin -10% Dextran 40 and centrifuged at 400 x g, 10 degrees C for 20 minutes. The results showed that the viability of nucleated cells post-thaw was (73.3 +/- 12.5)%, the CD34(+) cell content was (0.3 +/- 0.21)% for pre-freeze PCB and (0.45 +/- 0.36)% for post-t haw PCB. No significant difference for CFU-GM/-G/-GEMM counts was found between pre-freeze and post-thaw PCB. Thawed PCB contained in two compartments (20 ml and 5 ml) of a freezing bag showed similar viability and clonogenic capacity. Differential count of white blood cell was significantly changed. For post-thaw PCB, it was dramatically decreased for the percentage of granulocytes, and highly increased for the percentage of lymphocytes and monocytes. It was concluded that the condition for cryopreservation and thawing of PCB may be harmful to mature cells, and cells with large size, such as granulocyte, but suitable to lymphocyte and monocyte, especially for the cells with small size, such as CD34(+) cells.