We compared cryopreservation of peripheral blood progenitor cell (PBPC) products immediately and after overnight storage. There was no statistically significant difference in the groups regarding median CD(34)+ cell count of the product, storage duration at -80 degrees C, viability rates, neutrophil and platelet engraftment days. Overnight storage of products with leukocyte count >300x10(9)/l has longer leukocyte (P=0.03) and platelet (P=0.01) engraftment days compared to other groups. Overnight storage without adding any medium or plasma for the apheresis product with leukocyte count of less than 300x10(9)/l in a commercially available refrigerator can easily and safely be used in transplantation centers.