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the best indicator of the hematopoietic reconstitution capacity in vivo. Thus, this variable should be evaluated to estimate the clinical relevance of extended conservation period. Although these results should be considered preliminary because of the relatively small number of samples, these data do not support the proposal to extend the routine preprocessing storage period of UCB to 72 hours. Furthermore, they imply a deterioration of the UCB functional variables (loss of committed progenitors). Since this is a very important question, larger trials from different centers are necessary to definitely confirm these implications.