Abstract
The acidic protein called S100 and specific only for the nervous tissue has been localized mainly to the neuroglia by single diffusion agar precipitation in glass capillaries using antiserum. Application of the fluorescent antibody sandwich technique showed the specific fluorescence to be localized around the nuclei of oligodendrocytes and scattered throughout the glial membrane system. The neurons only showed specific fluorescence in the nuclei. The significance of these findings is discussed in relation to the rapid turnover of the protein S100.