Sixteen patients had atypical leukemia but the original bone-marrow specimens and blood smears were not diagnostic of leukemia. Thirteen were men, and all 16 were more than 50 years old. Clinical features were nonspecific in most cases. Initial manifestations that might have served as clues to a leukemic process were (1) monocytosis in the peripheral blood, (2) normoblasts in the peripheral blood in the presence of cytopenia, (3) marrow hypercellularity, frequently with hyperplastic or left-shifted myelopoiesis, (4) erythroid hyperplasia of the marrow, often with qualitative erythroid changes, and (5) acquired Pelger-Huët anomaly or changes in the granulation of myeloid cells. Survival time from onset of a known hematologic abnormality ranged from seven to 60 months, with only two patients surviving less than one year.