We examined the potential neurotoxicity of ca¡eine in vivo and in vitro. Intraperitoneal administration of ca¡eine (50 mg/kg, 3 times a day) produced neuronal death in various brain areas of neonatal rats 24 h later. Ca¡eine at doses 4 300 mM was also neurotoxic in murine cortical cell cultures. Ca¡eine-induced neuronal death was accompanied by cell body shrinkage and attenuated by anti-apoptotic drugs including cycloheximide, high potassium, and growth factors. Two necrotic pathways, excitotoxicity and oxidative stress, did not mediate ca¡eine neurotoxicity. The pro-apoptotic protease caspase-3 was activated to mediate neuronal death following exposure to ca¡eine. The present ¢ndings suggest that ca¡eine may cause caspase-3-dependent neuronal cell apoptosis in neonatal rat as well as in vitro. NeuroReport 13:1945^1950