['Uncontrolled-rate freezing (URF) techniques, which are fast and easy, could represent an attractive alternative to controlled-rate cryopreservation procedures which are time consuming and require high-level technical abilities. It was the aim of the present study to evaluate, on a routine basis, whether URF might spare primitive hematopoietic progenitors and maintain engrafting capacity.', 'One-hundred and nineteen peripheral blood progenitor cells (PBPC) collections from 104 patients with hematologic malignancies were cryopreserved in bags, with an URF procedure, in a cryoprotectant solution consisting of PBS, HSA and 10% DMSO and stored in liquid nitrogen. PBPC bags were tested before cryopreservation and at thawing for primitive (LTC-IC) and committed hematopoietic progenitors (CFU-Mix, BFU-E, CFU-GM) by means of long- and short-term culture assays, respectively. In addition, PBPC bags were evaluated for CD34+ cell numbers.', 'Although thawing was associated with a statistically significant reduction of the absolute number of nucleated cells, recovery of LTC-IC, CFU-Mix, BFU-E, CFU-GM and CD34+ cells was not affected by the freezing/thawing procedures. No adverse effects were reported at thawing and only mild transient reactions were recorded in 22 patients during reinfusion of cryopreserved PBPC. All the patients underwent myeloablative therapy followed by reinfusion of PBPC, and prompt and rapid hematopoietic recovery was obtained in all patients.'] Does uncontrolled-rate freezing of peripheral blood progenitor cells allow successful engraftment by sparing primitive and committed hematopoietic progenitors?