We have investigated the ability of a redox-active, ferrocene-containing cationic lipid [bis(11-ferrocenylundecyl)dimethylammonium bromide (BFDMA)] to transfect mammalian cells. This investigation sought to determine the range of conditions over which this lipid was capable of transfecting cells and whether the oxidation state of the ferrocenyl groups in this material, which can be controlled electrochemically, could be used to influence the extent of cell transfection. Transfection experiments conducted in the COS-7 cell line using a plasmid DNA construct encoding enhanced green fluorescent protein demonstrated that the extent of transfection depended significantly on both the concentration of BFDMA and whether the lipid was present in a reduced (+1) or an oxidized (+3) state. Subsequent quantitative characterization of cytotoxicity and gene expression using a plasmid encoding firefly luciferase demonstrated that a window of concentration existed over which reduced BFDMA was non-cytotoxic and yielded high levels of transfection, but over which electrochemically oxidized BFDMA yielded very low (background) levels of transfection. Taken together, these results demonstrate that the oxidation state of BFDMA, which can be controlled electrochemically, can be used to control the extent of cell transfection. These results could form the basis of transfection procedures that exploit the redox behavior of ferrocene-containing lipids to achieve active spatial and temporal control over transfection using electrochemical methods. Characterization of lipoplexes using dynamic light scattering demonstrated that reduced and oxidized BFDMA formed small aggregates (ca. 90 nm to 250 nm) at concentrations of lipid ranging from 2 micromolar to 10 micromolar. The influence of lipid oxidation state on the nature of physical interactions between BFDMA and DNA and the microstructures of the resulting lipoplexes will be discussed in the context of the striking differences observed in cell transfection.