Background: Mesenchymal stem cells (MSCs) have high proliferative anddifferentiation potential, in addition to their plasticity that makes thempromising candidates for cell therapeutic applications. Bone marrow (BM)harvest is still the main source of MSCs in spite of being traumatic andpainful. Clinical indications for peripheral blood (PB)-derived MSCs,which can be easily and safely harvested, are rapidly increasing.Objective: To isolate MSCs from BM and Leukapheresis product (afterstem cell mobilization) then to compare the viability, fold expansion andcell cycle status of MSCs derived from BM and mobilized PB.Methods: MSCs were isolated and cultured by the classical plasticadherence method from 10 BM and 10 leukapheresis samples. Theirviability, fold expansion and cell cycle status were compared.Results: The viability of BM derived MSCs was comparable to that ofleukapheresis derived MSCs (90.45% vs. 89.30%). The mean foldexpansion of MSCs derived from BM was greater than that ofleukapheresis derived MSCs (25.09 vs. 20.69) and correlated significantlywith the mean percentage of: cycling cells (p=0.032), quiescent cells(p=0.029) and apoptotic cells (p=0.014) after culture. These correlationscould not be detected in cases of leukapheresis derived MSCs.Conclusion: These results indicated a better quality of BM thanleukapheresis samples as a source of MSCs for clinical applications. Pooryield of the PB-MSCs may be due to the current methods of cellmobilization, isolation and culture which have not been optimized forMSCs. Further studies are needed to improve the quality of PB derivedMSCs prior to their potential use in clinical trials.