Chromatin structure-dependent binding of the DNA-specific dye 7-aminoactinomycin D (7-AMD) in leukemic and normal cells in bone marrow aspirates from childhood acute leukemia patients and patients without bone marrow neoplasia was assessed by multiparameter flow cytometry. Simultaneous staining with fluorescein isothiocyanate-labeled antibodies was needed in many cases for determination of the immunophenotype of the cells that exhibited differential binding of 7-AMD. 7-AMD binding was enhanced in normal (4 patients) and malignant (8 patients) myeloid cells, and was generally low in normal and leukemic lymphocytes and normoblasts. Four of 18 aspirates from 16 patients with acute lymphoblastic leukemia contained neoplastic cells with increased 7-AMD binding capability. The 7-AMD binding of the leukemic cells was not correlated to S-phase fraction (P = 0.07), but was significantly correlated to cell size as measured by forward angle light scattering (r = 0.49, P = 0.007). Patients with tumor cells exhibiting low 7-AMD binding at last aspirate survived significantly longer than the patients with leukemic cells binding high amounts of 7-AMD (P = 0.03). Neither cell size, S-phase fraction, nor ploidy status predicted patient survival in this small scale study.