Although no single model of the numerous animal models of brain tumors developed in recent years perfectly represents the spontaneous human tumors, different ones do have specific advantages for certain types of studies. Chemical induction in adult animals, transplacental chemical induction, viral induction, and transplantation are effective methods that allow choice of numerous histologic types of tumors which, to a greater or lesser extent, simulate human tumors. Reproducibility of location, cell type, and time of tumor appearances; expense; ability to grow in tissue culture; safety for personnel; trauma to brain; nature of vasculature, and amount of brain and tumor tissue available for examination are among the variables to be considered in choosing a model appropriate for a particular study.