Abstract—: The preparation and storage of platelet concentrate can be accompanied by activation of platelets and triggering of apoptosis, increasing the formation of platelet membrane vesicles and worsening the therapeutic properties of such preparations. However, the mechanisms for the regulation of apoptosis in platelets and the molecular composition of platelet membrane vesicles associated with this process have so far remained poorly understood. The aim of the work was to study proapoptotic caspase-3 and antiapoptotic microRNA-221 levels in platelets and platelet membrane vesicles during the storage of platelet concentrate preparations. The object of the study was samples of the pooled platelet concentrates (n = 6), taken from the containers on the second and seventh days of storage. Full length and activated caspase-3 were found in platelets and in fractions of membrane vesicles. The proportion of activated caspase-3 in platelets increased during storage. MicroRNA-221 was found in platelets, fractions of membrane vesicles, as well as in the extravesicular fraction. During storage, levels of microRNA-221 increased 8-fold (P = 0.004) in the fraction of membrane vesicles pelleted at 100 000 g. The results of the study indicate that the membrane vesicles released by platelets during storage contain mature microRNA-221 and the activated form of caspase-3.