Nucleolar organizer regions (NOR) are loops of ribosomal DNA(rDNA) which are transcribed by RNA polymerase I. They produce ultimately ribosome and protein. Thus they are believed to reflect nuclear activity. We applied silver colloid staining technique to human glioma to examine relationship between the mean number of Ag-NOR and histopathological grading. The mean number of Ag-NOR(${pm}$ S.E of the mean)were $1.17{pm}0.07$ in normal brain, $1.53{pm}0.25$ in astrocytoma, $2.37{pm}0.71$ in malignant astrocytoma, and $2.88{pm}0.41$ in glioblastoma multiforme. And there was a statistically significant difference among these. The results show that Ag-NOR technique is a rather simple and rapid method and will become a helpful tool for estimation of the proliferative potential of glioma.