We examined the changes in the early postmortem platelet count in postmortem blood and the reasons for these changes by counting the platelets, by performing in vitro hypostatic tests, by estimating the percentage of erythrocytes by volume in postmortem blood samples, by immunohistochemistry (anti-CD61, anti-fibrinogen), and by immunoelectron microscopy (anti-CD62, anti-CD63, anti-thrombospondin). The apparent initial increase in the platelet count in postmortem blood was found to be caused by hypostatic phenomena. The subsequent discontinuous decrease in the platelet count despite continuing hypostasis in the corpse can be explained in part by postmortem thrombolysis and the development of reversible platelet-platelet aggregates. The main point is, that changes in the postmortem blood environment cause potentially reversible adhesion of platelets to pre-adsorbed fibrinogen on erythrocytes. Thus the decrease in the number of platelets in postmortem blood is not attributable to postmortem clotting but to a decrease in the number of countable platelets in postmortem blood.