All organs in our body display 24-hour rhythms, regulated by interacting clock genes and proteins in the cells. All these organs and their rhythms are precisely tuned to each other to provide optimal support for our behaviour and performance. The brain contains a small group of nerve cells, called the suprachiasmatic nucleus (SCN), which coordinates the rhythms elsewhere in the body and also assures these rhythms are synchronized to the day-night cycle in the world around us. A disturbance in this system of clocks and rhythms can have a major impact on our well-being and health. One factor that may cause such disturbance in this so-called circadian system is stress. While the master clock in the SCN appears to be well protected against effects of stress, previous research showed that uncontrollable stress may shift the rhythms in peripheral organs. This new research in mice shows that effects of social stress on peripheral rhythms are tissue-specific and time-of-day dependent. It also shows that effects of stress accumulated with repeated or chronic stress. The shifts in peripheral rhythms could at least partly be explained by glucocorticoid stress hormones, which are released by the adrenal glands during stress. Although the hormone melatonin is generally seen as an important signal that is used by the SCN to coordinate peripheral rhythms, in the present studies it could not prevent the effects of stress.