Vitamin C has been suggested and disputed as an anti-cancer agent. Previous in vitro studies using either primary cell cultures from cancer patients or tumor cell lines have suggested that tumor cells with different lineages may have different sensitivities to ascorbic acid. In this study we report characterization of the effects of ascorbic acid on growth of two ascorbic acid sensitive and one ascorbic acid resistant lymphocyte tumor cell lines. The cytotoxic effects of ascorbic acid on the sensitive cell lines were time and dosage dependent. Furthermore, the energy state of the ascorbic acid sensitive cells was affected by the presence of ascorbic acid before the cells became apparently non-viable, as demonstrated by 31P nuclear magnetic resonance spectroscopy. The existence of these lymphocyte cell lines with varying sensitivities to ascorbic acid may provide a useful model system for further understanding of vitamin C action on cancer cells.