Biological markers in psychiatry.

Biological markers in psychiatry are defined as measurable and quantifiable indices of psychiatric disorders. Criteria for biological markers are discussed. The criteria for the assignment of a biological marker to the pathophysiology, pathogenesis, or etiology of a disorder are proposed. None of the biological markers described in the literature for depression, schizophrenia, alcoholism or anxiety as separate disorder fulfills the specified criteria. Most of them can at best be considered as biological markers of the aspecific processes of strain and stress. Free-floating anxiety is the clinical hallmark of strain.