BACKGROUND: Cord blood banking requires methods for shipping and storage. This study examines the influence of shipping via overnight courier on postthaw viability of cord blood. STUDY DESIGNS AND METHODS: Anticoagulated cord blood was divided with one sample diluted 1:1 using STM-sav (a storage solution) and the other undiluted. Units were shipped from Minneapolis to Memphis and returned, RBC-depleted, cryopreserved, stored for 14 days, and thawed. MNC counts, percent viable cells, quantity of CD34+ cells, and frequency of CFU-GM were measured. Temperature during shipment was continuously monitored. RESULTS: Preliminary studies showed the packing and processing protocol influenced the temperatures experienced during shipping. Samples achieved temperatures below 10°C within 4 to 8 hours with a few units dropping near or below 1°C with cold ambient temperatures. The MNC recovery, CD34+45+ recovery, and frequency of CFU-GM for samples that were shipped were comparable to those observed using static liquid storage. The postthaw viable cell recovery was greatest for storage and shipping times of 24 hours and decreased when the storage and shipping times were longer. CONCLUSION: Ambient conditions and the packing and processing protocol influence the temperature history of the sample. Samples stored beyond 24 hours in liquid storage and shipping exhibit a decreased postthaw recovery.