This article reviews research into the possible significance of disorders of the central 5-HT metabolism in the pathogenesis of recurrent vital depressions. The available data would seem to warrant the tentative conclusion that such metabolic disorders are indeed involved in a certain subcategory of vital depressions, and play a (possibly predisposing) role in the pathogenesis of these depressions. The use of 5-HT precurors in depressions is regarded as a potential asset, although the conclusion that real substitution therapy can thus be given would be premature.