The discovery of the genetic basis for circadian rhythms has expanded our knowledge of the temporal organization of behavior and physiology. Circadian rhythms regulate a wide variety of physiological and metabolic processes. The observation that the circadian gene network is present in most living organisms from eubacteria to humans, that most cells and tissues express autonomous clocks, and that disruption of clock genes results in metabolic dysregulation have revealed interactions between metabolism and circadian rhythms at neural, molecular and cellular levels. In this review we evaluate investigation of molecular timing may create new opportunities to understand the importance of biological clock.