Fluorescence histograms of CEM T-lymphoblasts and myeloblasts from AML patient H.M. stained with 5-(Sx8)-F in the presence of graded concentrations of NBMPR. Cells were treated with NBMPR at the concentrations shown before staining with 80 nmol/L 5-(Sx8)-F (CCRF-CEM cells) or 20 nmol/L 5-(Sx8)-F (myeloblasts from patient H.M.) and analysis by flow cytometry. Each fluorescence histogram represents the analysis of 10,000 cells. With increasing concentrations of NBMPR, the decrease in fluorescence indicates a progressive blockade of 5-(Sx8)-F sites on the es transporter. Left series, CEM cells; right series, myeloblasts from patient H.M.