In this article the value of the tyramine conjugation test (TCT) as a predictor of the response to antidepressive medication is reviewed. The TCT seems of little discomfort for the patient, is easy to perform and is suggested to have a high sensitivity and specificity. In addition, there are indications that a decreased tyamine conjugation could be a traitmarker for the vulnerability of depression. Hypotheses concerning the, as yet unclear etiology of the decreased tyramine are reviewed.