In mammals, the principal circadian oscillator resides in the hypothalamic suprachiasmatic nucleus. However, the basic components and the ability to generate a circadian rhythm are also characteristic of most peripheral tissues and some cell lines. In our present study, we show that the rat C6 glioma cell line displays circadian oscillations of reporter luciferase bioluminescence driven by the mouse Pert promoter and of clock-related gene transcripts. Per2::luc expressing C6 cells display circadian rhythm in their bioluminescence levels for more than seven days. In addition, clock and clock-controlled genes show dynamic circadian oscillation in C6 cells after exposure to dexamethasone. It is also significant that Per1 is not induced in C6 cells by a calcium ionophore, which is in stark contrast to Rat-1 cells. The C6 glioma cell line has therefore the potential to be a useful tool in future investigations of the underlying molecular machinery of the circadian clock. (c) 2006 Elsevier Inc. All rights reserved.