uman glioma rarely metastasizes outside the cranium but sometumors are highly metastat ic to thebrain. We developed an in-vivo modelinnude mice to study the metastatic mechanism to prevent glioma but allowmelanoma to pass through the blood-brain barrier. The glioma cellssuspension and melanoma cells suspension were injected in internal carotidartery of nude mice respectively.The glioma group resulted in metastatictumors invading the skull without passing the blood-brain barrier into thebrain. In the melanoma group tumor metastasized into the brain throughblood-bra in berrier in all cases.The tumor metastasis outside or inside thebrain is likely due to its ability to emigrate through the blood-brainbarrier. Direct carotid artery injection in nude mice is technically quitedifficuIt, but the animal model is useful to define cellular genetic, andimmunogical factors involving metastatic brain.