Two children presented with Ph1-positive leukemia, confirmed by Giemsa banding as 22q-. One child showed an initial presentation characteristic of acute lymphoblastic leukemia, followed by development of chronic myelocytic leukemia 2 yr later. A second child presented in blast crisis. Both patients showed blast cells possessing both lymphoid and myeloid characteristics, as demonstrated by histochemical, biochemical, or surface receptor properties of each cell series. The evidence provided supports the assumption of mixed lymphoid-myeloid properties of blast cells in chronic myelocytic leukemia in children. Detailed study of the leukemic cells may aid in the understanding of complex stem cell relationships and suggest more effective therapeutic approaches.

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