Herbal products are being increasingly used as dietary supplements and therapeutic agents. However, much more research must be performed in order to determine the biological basis for their putative clinical effects. We tested the effects of milk thistle (Silybum marianum) extract on the differentiation and survival of cultured neural cells. Milk thistle enhanced nerve growth factor (NGF)-induced neurite outgrowth in PC-12 neural cells and prolonged their survival in culture. Milk thistle extract also protected cultured rat hippocampal neurons against oxidative stress-induced cell death. Our data demonstrate that milk thistle extract can promote neuronal differentiation and survival, suggesting potential benefits of chemicals in this plant on the nervous system.