In this study, we show that most glial cell subtypes of the adult Drosophila CNS express PER in a manner suggesting that circadian clock may function in these cells. These glial subtypes include perineurial glia, subperineurial glia, cortex glia, ensheathing glia of the central brain and the giant glia located in the medulla. While rhythmic PER expression in the medulla was reported previously (Suh and Jackson, 2007; Gorska-Andrzejak et al., 2009), our data suggest clock function in several other types of glial cells. However, the astrocyte glia appear to be an exception as we did not detect PER protein in these cells at either time point examined.