Abstract
The ultrastructural findings in the peripheral blood cells of two young patients with acute mixed-lineage leukemia are presented. While in one of the patients, characteristics typical for both the lymphoid and myeloid cell series were observed in single cells, in the second patient, in addition to similar cells, lymphoid and myeloid blasts were also found. The contribution of electron microscopic analysis in establishing the definite diagnosis of this subtype of acute leukemia is discussed.