The circadian cycle: is the whole greater than the sum of its parts?

The term 'circadian rhythm' describes an oscillatory behavior in the absenc e of exogenous environmental cues, with a period of about a day. As yet, we don't fully understand which biological mechanisms join together to supply a stable and self-sustained oscillation with such a long period. By chippi ng away at the molecular mechanism with genetic approaches, some common fea tures are emerging. In combining molecular analyses and physiological exper iments, those features that are crucial for structuring a circadian day cou ld be uncovered.