We report a systematic investigation of caffeine-induced dissociation of ethidium (Et) cation, a potential mutagen. Time-resolved fluorescence studies are consistent with a mechanism where caffeine-Et complex formation in bulk solution drives the dissociation of DNA-bound Et. Temperature-dependent picosecond-resolved studies show the caffeine-Et complex to be stable over a wide range of temperature, within and beyond the normal physiological limit. A combination of NMR spectroscopy and dynamic light scattering experiments allowed us to propose a molecular model of the caffeine-Et complex. Caffeine-induced extraction of Et from whole cells was also performed on squamous epithelial cells collected from the inner lining of the human mouth, A549 (lung carcinoma), A375 (human skin), RAW (macrophage), and Vero (African green monkey kidney epithelium) cell lines. Interestingly the efficiency of caffeine in extracting Et has been found to be dependent on cell types. Our results both in vitro as well as ex vivo provide important clues about the efficiency and mechanism of caffeine as a potential antimutagenic therapeutic agent. © 2011 American Chemical Society.