an unusual form of myelopoietic disease that is characterized by a seemingly uncontrolled proliferation of megakaryocytes in the bone marrow, and sometimes by the presence of a considerable number of megakaryocytes in the circulating blood. When bone marrow is examined at various intervals in some instances of chronic myelocytic leukemia, the proliferation of megakaryocytes is more prominent than that of the granulocytes; at such times, the circulating blood may contain megakaryocytes or fragments of megakaryocytic nuclei and cytoplasm, or both, amounting to as much as 5 or 6% of the total number of leukocytes.