The neurobiological alterations commonly found in affective disorders (e.g., alterations in the nocturnal sleep profile, dysfunction of the hypothalamic-pituitary-adrenocortical system) gradually recover with improvement of the depressive syndrome. Their persistence during full clinical remission, however, is associated with an increased risk for relapse and, thus may represent trait markers for affective disorders. In order to test this hypothesis, we designed a prospective study in which healthy first-degree relatives (high-risk probands; HRPs; n = 54) of patients with an affective disorder are investigated by means of polysomnography, the combined dexamethasone and corticotropine-releasing hormone (DEX-CRH) test and a variety of psychometric scales. In the present part of the study (index assessment), these HRPs, as a group, showed depression-like alterations in both the sleep pattern and the DEX-CRH-test outcome; furthermore, their psychometric profile was characterized by elevated scores on the scales assessing "rigidity" and "autonomic lability". On a single-case level, 35% of the HRPs were identified as conspicuous (depression-like) in at least two of the three areas investigated. A decision of whether or not this "conspicuousness" indeed represents a trait marker for affective disorders can be reached when the follow-up part of the study has identified those HRPs with their respective premorbide status who have developed an affective disorder in the meantime.