The circulating megakaryocytes (MK) in the central venous blood of rats during haemorrhagic shock have been studied. Nucleopore polycarbonate membranes with a pore size of 5 microns were used to isolate circulating MK. Different morphologic types of MK were analysed. The results showed an increased number of MK migrating from the bone marrow to blood and confirm that circulation MK are a normal physiologic component of blood. The number of the rise during haemorrhagic shock, especially large MK and MK with scant cytoplasm ("naked nuclei" MK).