A t(1;3)(p36;q21) translocation was found in bone marrow samples of two patients with hematologic disorders. One patient had a myelodysplastic syndrome evolving into acute nonlymphocytic leukemia (ANLL) M1 and the second patient had ANLL-M6 secondary to treatment for Hodgkin's disease. Because myelodysplastic syndromes and secondary leukemia are stem cell disorders, the t(1;3)(p36;q21) appears to be a chromosome abnormality in malignant myeloid stem cells.