We investigated which glia subtypes express the circadian clock protein PER in a manner similar to that of the pacemaker neurons and whether the relative amounts of PER signal change with age. To label specific glial cells, we employed the GAL4/UAS system (Brand and Perriman, 1993) using GAL4 lines to drive GFP expression in subtypes of glia with specific location and function in combination with immunocytochemistry to measure PER levels. It has been reported that PER expression in lateral and dorsal pacemaker neurons are equally strong in young and old Drosophila brains (Luo et al., 2012); therefore, the presence of PER staining in these neurons was used as a positive control. These cells have rhythmic PER expression with high levels at ZT22 and lack PER at ZT10 in wild type flies (Long et al., 2014); therefore, we selected these time points to examine glial cells.