21 human primary brain gliomas and 11 human menigiomas were examined with RNA dot blot hybridization for the expression of p53, Rb and c-myc gene. It was found that the level of p53 gene expression is lower in 48.4% (15/31) of the tumors tested than that of normal brain tissues; the level of Rb gene expression is lower in 21.9% (7/32) for the tumors tested than that of normal tissues; and the level of c-myc gene expression is higher in 71.9% (23/32) for the tumors tested than that of normal tissues. Interestingly, in 13 of the tumors tested, the level of p53 gene expression is lower and the level of c-myc gene expression is higher. These results suggested that the expressive decrease of p53 gene and the expressive increase of c-myc gene are relative to the generation of human primary brain tumor.