NAD⁺ plays important roles in various biological processes. It has been shown that NAD⁺ treatment can decrease genotoxic agent-induced death of primary neuronal and astrocyte cultures, and NAD⁺ administration can reduce ischemic brain damage. However, the effects of NAD⁺ treatment on tumor cell survival are unknown. In this study we found that treatment of NAD⁺ at concentrations from 10 microMole to 1 mMole can significantly decrease the survival of various types of tumor cells such as C6 glioma cells. In contrast, NAD⁺ treatment did not impair the survival of primary astrocyte cultures. Our study has also indicated that oxidative stress mediates the effects of NAD⁺ on the survival of tumor cells, and P2X7 receptors and altered calcium homeostasis are involved in the effects of NAD⁺ on the cell survival. Collectively, our study has provided the first evidence that NAD⁺ treatment can decrease the survival of tumor cells by such mechanisms as inducing oxidative stress. Because NAD+ treatment can selectively decrease the survival of tumor cells, NAD⁺ may become a novel agent for treating cancer.