AbstractChromosome analyses in leukemias and cancers have yielded a body of cytogenetic information which has led to the hypothesis that specific (primary) chromosomal abnormalities exist in specific types of leukemia and cancer, findings of value in the diagnosis, prognosis, and classification of each condition (1-6). In hematopoietic neoplasia such nonrandom chromosome abnormalities are often and consistently associated with a particular disease process, making it possible to subdivide the acute leukemias and myelodysplastic syndromes into distinct categories. Furthermore, the primary cytogenetic change may serve as an independent variable in the prognosis, apparently unrelated as to how these diseases are classified according to the criteria of the French-American-British (FAB) Cooperative Group (7).