Abstract
The paper by Greenberg et al. in this issue of the Journal contributes data to a long standing, but until recently dataless, controversy: whether leukemia is due to a mutation in a single cell resulting in the re-population of the hematopoietic system by progeny of this "bad seed" (clonal theory), or whether the evident cellular abnormality in many leukemias is due to external and potentially reversible influences on hematopoietic cells (externalinfluence theory). The time-honored example given in support of external influences is the finding of morphologically and functionally abnormal cells in pernicious anemia, a disease that some investigators once considered . . .