Marked patient-to-patient variation is observed when blood or marrow from AML patients is examined using colony methods in culture. Concentrations of the progenitors of colonies change with time during the course of the disease. We asked whether blast progenitor properties were more stable. We measured blast cell self-renewal and drug sensitivity (adriamycin and cytosine arabinoside) repeatedly in the courses of seven AML patients. These properties were found to be stable or slowly evolving. We conclude that capacity for renewal and sensitivities to certain chemotherapeutic drugs are heritable characteristics in leukemic clones.