Clinicians have known for years that organs function at different rates — the heart beats, kidneys transport ions and electrolytes, the liver metabolizes lipids, sugars, and amino acids differently over the course of the day — and have used this knowledge to design more effective drug regimens for patients. A better understanding of what drives those local rhythms, and how they go wrong, could aid physicians’ efforts. Now a study, among the first to explore timing mechanisms outside the brain, could have a broad impact on the burgeoning fields of circadian medicine and postgenomic science. Researchers from Harvard Medical School and the Harvard School of Public Health found that the daily rhythms of the body — once thought to be strictly governed by a master clock lodged in the brain — appear to be driven to a remarkable degree by tiny timepieces pocketed in organs all over the body. The study was reported in the April 21, 2002 Nature online.