A case of chronic erythroleukemia is reported in which a picture of chronic granulocytic leukemia preceded the erythremic proliferation by one to three years. The patient was followed throughout his entire 10-year course and the clinical impressions were confirmed initially by biopsy and eventually at necropsy.

The rare examples of this occurrence usually cited in the literature are reviewed and briefly discussed. In every case the development of erythremia was preceded by radiation therapy for the leukemic dyscrasia.

A set of criteria for evaluating such cases in order to provide definite evidence for this sequence of events is suggested.

The transformation of chronic granulocytic leukemia into polycythemia vera or chronic erythroleukemia lends further support to the concept of fundamental similarity and close inter-relation of these myeloproliferative disorders.

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