Background: Infusion of cryopreserved and non-cryopreserved hematopoietic progenitor cells (HPC) is associated with a broad variety of symptoms. In this study, we have investigated infusion-related toxicity regarding temperature of cryopreserved autologous peripheral blood progenitor cells (PBPCs) transplanted in 31 and allogeneic non-cryopreserved PBPCs in 4 patients receiving high dose chemotherapy and stem cells transplantation for hematological malignancies., Study Design and Method: A 24h ECG-Holter recording system was used to obtain cardiac arrhythmias. Two milliliters HPC were collected from entrance site of venous access to evaluate the temperature of infused HPC., Results: We have detected arrhythmias in 17 (48.58%) of our patients before, during and after infusion. Median temperature of the infusat was 21 degrees C (18-28.2). Arrhythmias during infusion were detected in 8 (22.85%) patients. The temperatures of infused HPCs were not statistically different in group with and without arrhythmias as 22 degrees C and 21 degrees C, respectively (P>0.05). And also, volume, contents [dimethylsulphoxide (DMSO), red blood cells (RBC), platelet (PLT), and total nucleated cell (TNC)] of product, and rate of infusion speed did not have any effect on arrhythmias., Conclusion: As a result of this study, we have concluded that the temperature of HPC does not cause any systemic hypothermia and does not have any relation to arrhythmias detected during infusion.