BACKGROUND: An altered nocturnal sleep pattern and a dysfunction of the hypothalamic-pituitary-adrenocortical system are neurobiological abnormalities typical for depression. A persistence of these neurobiological alterations during remission has been shown to be associated with an increased risk for a relapse. However, it remains unclear whether these persisting abnormalities are trait markers indicative of an increased vulnerability for affective disorders or only represent 'biological scars' acquired during past episodes. Thus, respective examinations need to be performed in the premorbid state in order to answer this open question. METHODS: In the present article we have summarized the various results of the index investigation of a prospectively designed study in which we investigated 54 healthy first-degree relatives (high-risk probands; HRPs) of patients with an affective disorder using polysomnography, the combined dexamethasone corticotropine-releasing hormone (DEX-CRH) test and psychometric measurements. RESULTS: In the cross-sectional part of this study the HRPs, as a group, exhibited a 'depression-like' sleep EEG profile and DEX-CRH test result, while their psychometric profile was characterized by elevated scores on the measures 'Rigidity' and 'Autonomic lability'. On an individual level, 35% of the HRPs were identified as conspicuous in at least two of the three areas under investigation. CONCLUSIONS: The question of whether these abnormalities do indeed reflect trait markers indicative of an increased vulnerability for depression will be answered by the longitudinal part of the study that allows for the retrospective identification of the premorbid status of those HRPs who develop an affective disorder during the follow-up period.