ABSTRACT
A case of megakaryoblastic transformation of a myeloproliferative disorder presenting initially as chronic granulocytic leukaemia with an intermediate phase of essential thrombocythaemia in a Chinese woman of 65 years is reported. The diagnosis of megakaryoblastic crisis was based on morphological, cytochemical and immunocytochemical features present in blast cells in the blood, together with cytochemical and ultrastructural features of micromegakaryocytes and megakaryoblasts which were predominant in the marrow. A literature review showed newer refinements in diagnosis such as ultrastructural platelet peroxidase and additional immunologic techniques employing antisera against further platelet products. The response to treatment remains uniformly poor.