Human platelets contain caspases and caspase activators. Whole-cell lysates (25 μg protein) were subjected to SDS-PAGE and Western blotting with antibodies against apoptotic proteins (APAF-1, cytochrome c, caspase-9, caspase-3, DFF45), a platelet marker (gpIIb), a T-cell marker (CD3), and actin as a loading control. The presented blots were performed with lysates from platelet concentrates. Comparable results were obtained with freshly isolated platelets.