Abstract: The fine structure of micromegakaryocytes were observed under electron microscope in blood and/or bone marrow specimens in six patients with myeloproliferative disorder.Abnormal ultrastructures of the micromegaka-ryocytes were studied.The 3 main morphological charactersties of megaka-ryocte,as the α-granules,demarcation membrane and the special shape of pseudopia,may serve as important distinguishing characteristies in the classification of micro-megakaryoctes.Five types of abnormal micromegaka-ryocytes could be seen under electron microscope.

Key words: mieromegakaryocyte, electron microscopy, ultrastructure