A comparative immunohistological study of the neurone-specific gamma gamma enolase and alpha alpha enolase, demonstrates the exclusive neuronal localization of gamma gamma enolase and its absence from glial cells. In contrast, alpha alpha enolase is located in astroglial cells. The validity of gamma gamma enolase as a neuronal marker and alpha alpha enolase as an astrocytic marker, is confirmed both by a double labelling technique, using antibodies to alpha alpha and to gamma gamma revealed with fluorescence or peroxidase in the same tissue sections, and by immunoelectronmicroscopy.