The intergeniculate leaflet (IGL) of the lateral geniculate complex is marked by the presence of neuro-peptide Y-containing neurons that project to the suprachiasmatic nuclei (SCN) of the hypothalamus. In the present study, we demonstrate that both the IGL and SCN in the hamster and rat are specifically delineated by the presence of glial fibrillary acidic protein-like immunoreactivity. This is significantly greater than in most other diencephalic regions and is particularly dense in the hamster brain. These observations suggest that glial-neuronal interactions may participate in circadian rhythm generation and regulation.