The auditory system is permanently open - even during sleep. Its quick and overshooting excitations caused by noise signals are subcortically connected via the amygdala to the hypothalamic-pituitary-adrenal-axis (HPA-axis). Thus noise causes the release of different stress hormones (e.g. corticotropin releasing hormone: CRH; adrenocorticotropic hormone: ACTH) especially in sleeping persons during the vagotropic night/early morning phase. These effects occur below the waking threshold of noise and are mainly without mental control. Animal experiments show noise-induced changes in sensitivity of cellular cortisol receptors by increase of heat-shock proteins, and ultrastructural changes in the tissue of the heart and the adrenal gland. Increased cortisol levels have been found in humans when exposed to aircraft noise or road traffic noise during sleep. The effects of longer-lasting activation of the HPA-axis, especially long term increase of cortisol, are manifold: immuno suppression (e.g. eosinopenia), insulin resistance (e.g. diabetes), cardiovascular diseases (e.g. hypertension and arteriosclerosis), catabolism (e.g. ostoeporosis), intestinal problems (e.g. stress ulcer) etc. Even worse may be the widespread extrahypothalamical effects of CRH/and/or ACTH which have the potential to influence nearly all regulatory systems, causing for example stress-dysmenorrhea etc. as signs of disturbed hormonal balance.