Released annexin V, an intracellular platelets glycoprotein, was used to determine the cellular injury which occurred during storage of platelet concentrates. Twenty-eight units of leuco-reduced apheresis platelet concentrates, obtained without leucocyte filtration, were analysed. Released annexin V showed a significant correlation with EDTA-induced shape changes of platelet (r = 0.62, P < 0.01) while poor correlation was found between released annexin V and pH or MPV. The combination of released annexin V with dMPV provides excellent markers of the platelet storage lesion for quality monitoring, based on morphological/functional integrities and cellular injury, which are of direct relevance to clinical efficacy of platelet concentrates.