A new method was developed that reduces the intracellular iron content of cells grown in serum-containing culture without involving the significant uptake of iron-chelating agents into cells. Negatively charged bathophenanthrolinedisulfonate (BPS), together with ascorbate, caused cells to lose much of their cellular iron without causing much depression in HL-60 or H9c2 (2-1) cell proliferation over a 48-h period. When added to serum supplemented RPMI-1640 culture media, BPS and ascorbate efficiently reduced and competed for iron in Fe(III) transferrin to form Fe(II)(BPS)3. The reaction also occurred with purified human iron-transferrin. When cells were incubated with growth medium containing serum that had been treated with BPS and ascorbate for 24 h, little or no BPS2- or Fe(II)(BPS)(4-)3 entered the cells, according to direct measurements and in agreement with the highly unfavorable 1-octanol/water partition coefficients for these molecules. However, iron was mobilized out of both cell types. After 24 h incubation of cells in this medium, there was no change in the activities of catalase and superoxide dismutase, or in the concentration of glutathione. Glutathione peroxidase was elevated 9%. Using HL-60 and H9c2 (2-1) cells made iron deficient with BPS and ascorbate, HL-60 cells grown in defined-growth media in the absence of iron-pyridoxal isonicotinoyl hydrazone, or Euglena gracilis cells maintained in a defined medium that was rigorously depleted of iron, it was shown that the cytotoxicity of adriamycin is markedly dependent on the presence of iron in each type of cell. Similar results were obtained when HL-60 cells were grown in RPMI-1640 culture medium and serum that had been incubated for 24 h in BPS and ascorbate and then chromatographed over a Bio-Rad desalting column to remove small molecules including BPS, ascorbate, and Fe(II)(BPS)3.