This study compares the cryopreservation of PBSC by means of HES 3% + DMSO 5% ina mechanical freezer with the cryopreservation of PBSC by means of DMSO 10% in an automated rate controlled freezer. The cells harvested from the same patient were divided in two equal parts and frozen according to both methods. Cryopreservation with HES +DMSO is better than DMSO alone in terms of viability (p<0.001) and Granulocyte Macrophage Colony Forming Unit (GM-CFU) activity (p<0.05). The freezing curves differ essentially in the slope down after the surfusion peak. However, surfusion peaks are similar in both conditions. The relevance of mechanical freezing is the saving of time and the safety of such a procedure.