Background and Objectives: Hyperconcentration of platelets may lead to platelet activation and loss of platelet function. Materials and Methods: Platelet activation following hyperconcentration was assessed using flow-cytometric detection of platelet P-selectin expression and platelet swirling. Results: Platelet hyperconcentration led to a minimal increase in P-selectin expression and no differnce in platelet swirling. Conclusion: Hyperconcentration was not associated with a clinically significant change in platelet activation and had no significant effect on platelet quality as detected by pH and platelet yield.