The master circadian pacemaker of the suprachiasmatic nuclei coordinates behavioral and physiological rhythms via synchronization of subordinate peripheral oscillators in the central nervous system and organs throughout the body. Among these organs, the adrenal glands hold a prime position because of their regulatory influence on numerous physiological functions via rhythmic secretion of catecholamines and corticoid hormones into the bloodstream. In this report, the authors perform whole genome microarray hybridization to characterize the circadian transcriptome of the murine adrenal. They show that ~5% of the mouse genome is under circadian control in this gland. Using gene ontology analysis, they identify classes of transcripts that may synchronize adrenal hormone production. The authors' expression profiling also revealed that multiple histone genes implicated in either DNA replication or transcriptional regulation are clock controlled, suggesting a novel way by which the circadian clock may regulate the chromatin state.