The key objective of this study was to examine whether leucocyte depletion generated or removed platelet-derived microvesicles in platelet concentrates for transfusion. Three in-process leucocyte removal filters for pooled buffy coat derived platelet concentrates, i. e. negative charged polyester, positively charged polyester, and non-charged polyurethane, were compared. The effects of three major leucocyte depletion technologies currently in use in the UK, i. e. Cobe LRS and Haemonetics MCS+ LD apheresis, and filtration of pooled buffy coat derive platelets, on platelet microvesiculation were also examined. Furthermore, the effects of various leucocyte filters and leucocyte depletion technologies on platelet activation and the activation of coagulation/complement systems were investigated. The procoagulant and anticoagulant properties of microvesicles isolated from platelet concentrates were explored. Leucocyte filtration of pooled bully coat derived platelet concentrates by all three filters did not have a net effect on the level of microvesicles. All three leucocyte depletion technologies gave similar values of microvesicles on day 1, but on day 5 MCS+ LD apheresis showed the lowest value, whilst Cobe LRS apheresis and buffy coat methods were equivalent. Among the three filters, the negatively charged filter activated the coagulation system as measured by kallikrein-like and thrombin-like activities, but removed some activated complement C3a, whereas the positively charged filter generated C3a. Among the three leucocyte depletion technologies, platelets prepared by Cobe LRS showed the lowest degree of activation of the coagulation system. However, both Cobe LRS and MCS apheresis showed higher levels of C3a than filtered buffy coat derived platelets. The microvesicles isolated from day 1 platelet concentrates could act as a catalytic surface for both the coagulant and anticoagulant reactions as measured by the formation of prothrombinase complex and the inactivation of FVa by activated protein C. The microvesicles isolated from day 5 platelets showed an increased procoagulant activity, whereas the anticoagulant activity substantially diminished.