PURPOSE: Cryopreservation has been the standard method of storing hematopoietic cells for the past 20 years, but this prdegrees Cedure is laborious and expensive. So, we evaluated the hematopoietic recovery of stored PBSCs at 4degrees C for a variable storage period MATERIALS AND METHODS: Eight leukapheresis products were kept unprdegrees Cessed at 4degrees C for 96 hours. To evaluate the effect of storage period on the hematopoietic recovery of PBSCs, assays for viability of mononuclear cells (MNCs), CFU-GM colony counts and CD34 cell counts were performed every 24 hours after PBSC collection. We tried to compare hematopoetic recovery of stored PBSCs at 4degrees C with that of cryopreserved PBSCs by using repeated measures ANOVA. RESULTS: Viability of MNCs, CFU-GM colony counts and CD34 cell counts were monitored at 24 hour, 48 hour, 72 hour and 96 hour after PBSC collection. Data are expressed as percentage of baseline value and shown as mean s.d.; MNCs viability (96+/-2%, 94+/-2%, 92+/-2%, 88+/- 3%), CFU-GM colony counts (87+/-10%, 79+/-11%, 65+/-13%, 56+/-15%), and CD34 cell counts (93+/-13%, 93+/-12%, 88+/-14%, 85+/-19%). After storing PBSCs at 4degrees C for 96 hours, viability of MNCs and CFU-GM colony counts were significantly reduced (p<0.05) except CD34 cell concentration (p>0.05). Prdegrees Cedures of controlled-rate freezing and thawing resulted in a notable loss of viability (77+/-9%) and CFU-GM colony count (71+/-29%). CFU-GM colony counts of 72 hour-stored PBSCs at 4degrees C was similar to those of cryopreserved PBSCs. CONCLUSION: If G-CSF mobilized PBSCs are stored at 4degrees C in less than 72 hours after collection, those hematopoietic recovery would be comparable to that of cryopreserved stem cells which are achieved by the rate-control freezer.