Development of a Questionnaire for Endogenous Regulation-a Contribution for Salutogenesis Research Introduction: Objective of this study was to develop a questionnaire for endogenous regulation (eR) and to evaluate its relevance in clinical and preventive medicine. The inventory included items about sleeping and waking, orthostatic regulation, thermoregulation, and circadian well-being. Methods: 158 age-matched women with diabetes (1/2, n = 53), breast cancer (n = 52) and healthy controls (n = 53) filled in the Havelhohe constitutional questionnaire (HKF1.0), and a 24-h-Oxford-FD3-ECG was recorded. Results: We developed a twelve-items scale for eR, which is according to test theory an objective and reliable instrument (Cronbach-alpha r(alpha) = 0.71, retest reliability: r(t) = 0.83). The validity analysis confirmed that the breast cancer and diabetic group show a lower eR than the control group (both p < 0.001). Furthermore, high eR is correlated with a 'rare tendency to feel quite low', 'less allergies', 'less period pains', and a I shorter duration of breast cancer'. Therefore eR can be regarded as a marker for health and well-being. High eR correlates as well with personality traits as morningness, 'needing less time for thinking through', 'being less unsure at important decisions', and 'being less confidential'. We can show first correlations between eR and the rhythmical marker 'nightly pattern predominance'. With both methods we are achieving for women until 60 years a satisfying discrimination between breast cancer and healthy individuals. Conclusions: We are achieving a first validation of our scale of endogenous regulation. Further studies for the evaluation of the conceptual, clinical, rehabilitative, and preventive medicine relevance of eR are necessary.