Background Currently platelet concentrates (PC) are collected using different synthetic materials and different centrifugation/leucocyte-removal processes Upon exposure to artificial surfaces and high centrifugation forces blood cells can undergo various levels of stress-induced, cellular activation/fragmentation and release reactions which may not only influence the extent of the platelet storage lesion but may also contribute to poor clinical effectiveness of the PC and transfusion reactions Materials and methods. An array of assays, used for quality control of PC, was performed in two different groups of PC prepared from random donor plasma on days I 3 and 5 of storage The group 1 PC were not leucoreduced while the group 2 PC underwent prestorage leucoreduction using a PL50E filter As current recommendations for the evaluation of PC include the measurement of platelet activation, in this study CD62P on platelet membrane was measured Furthermore, in vitro studies indicate that sHLA antigens may modulate immune competent cell function so, the presence of sHLA-1 in blood components is considered a marker of immunological reactivity and this too was measured Results The levels of CD62P and sHLA-1 were significantly towel in leucoreduced PC than in non-leucoreduced ones However the overall rate of increase of sHLA-1 during storage was taster in the leucoreduced group of PC No significant differences were detected regarding other assays of quality Conclusion Based on our findings, leucoreduced PC differ from non-leucoreduced ones in terms of some specific markers such as CD62P as a marker of platelet activation and sHLA-1 as a marker of immunological reactivity Pre-storage leucofiltration, followed by storage in currently used plastic bags is a sate procedure for PC for up to 5 days The available leucoreduction technologies are not, however sufficiently robust to completely abrogate transfusions reactions, and improvements are required to reach the goal of optimised yield and minimal transfusion reactions with platelet therapy