The procedure of autologous peripheral blood stem cell transplantation (autoPBSCT) requires cryopreservation of cells in a mixture containing dimethyl sulfoxide (DMSO). DMSO is necessary to secure cell viability, however, its infusion may be toxic to stem cell recipient. The aim of this study was to prospectively evaluate the impact of DMSO concentration on engraftment after autoPBSCT.One-hundred-fifty patients were randomly assigned to one of three study arms; their leukapheresis products were cryopreserved in 10%, 7.5% or 5% DMSO. The study groups did not differ with regard to the diagnosis (mainly lymphomas and multiple myeloma), age, conditioning regimen, and the number of transplanted hematopoietic stem cells. 143 patients were treated with autoPBSCT. The frequency of adverse effects during and shortly after infusion was the lowest in 5% DMSO arm (p = 0.02 compared to 10% DMSO). 4 patients died due to infection before the engraftment. The median time to leukocyte and neutrophil recovery was 10 days in all study groups (p = 0.36 and p = 0.2). As well, the median day of platelet recovery was the same for all DMSO concentrations and equaled 15 days (p = 0.61).In view of these results, 5% DMSO mixture may be considered a new standard in cryopreservation of hematopoietic stem cells.