Eight patients with clinical bleeding problems have evidence for platelet storage pool disease as they present with impaired platelet aggregation and secretion with low concentrations of ADP and collagen and an absence of second phase aggregation with epinephrine. Electron microscopy analysis further showed a reduced but not absent amount of platelet dense granules, and CD63 staining was decreased compared to healthy controls. The presence of alpha granules and CD62P expression after platelet activation was normal. This work aimed at identifying differentially expressed proteins in the platelet releasate and its remaining pellet after activation with A23187 and TRAP in patients and controls using DIGE-based proteomic technology. We identified 44 differentially expressed proteins in patients and the altered expression for some of them was confirmed by immunoblot analysis. Most of these proteins belong to the class of cytoskeleton-related proteins. In addition, 29 cytoskeleton-related genes showed an altered expression in platelet mRNA from patients using a real-time PCR array. In conclusion, our study shows that the dense granule secretion defect in patients with platelet storage pool disease is highly heterogeneous with evidence of an underlying cytoskeleton defect.