A sample of AML present in a bone marrow aspirate (case no. 3) was stained with CD34 (APC). AC133-PE and CD90-FITC MoAbs, as well as isotype control antibodies conjugated with FITC, PE, or APC. Upper left, the gate on forward scatter v side scatter (R1) that contained the leukemia blast cell population is shown on a 10% probability contour plot. Upper right, the pattern of CD34 and AC133 expression on cells gated for R1 is shown; 46% of the cells were contained within the upper right quadrant (R2). Lower left, the pattern of IgG-APC and IgG-PE isotype MoAb expression on the R1 population. Lower right, the pattern of CD90 expression on the leukemia cell population (gated on R1 and R2) compared with the pattern of staining using an isotype control antibody (- - - -).