Staining patterns of a normal donor and diagnostic AML samples. Representative flow cytometric staining patterns of ALDH activity by side scatter (SSC) are displayed for CD34⁺CD38⁻ cells isolated from: (A) a normal donor, (B) a patient (patient 9) with t(8;21) AML, (C) a patient (patient 1) with Inv16 AML, and (D) a patient (patient 17) with normal cytogenetic (cyto) AML. The AML samples, but not the normal marrows, contained a discrete CD34⁺CD38⁻ALDH^int population (circled). In the patients with CBF AML, this CD34⁺CD38⁻ALDH^int population was essentially completely leukemic by FISH. The CD34⁺CD38⁻ALDH^low population from the CBF AMLs was also almost entirely leukemic by FISH. In contrast, the small CD34⁺CD38⁻ALDH^high populations (boxed) from CBF AML patients lacked the leukemia-specific FISH marker. The percentages of CD34⁺CD38⁻ cells composed of the CD34⁺CD38⁻ALDH^int and CD34⁺CD38⁻ALDH^high populations are listed on each dot plot.