Depression is a leading cause of disability and premature death, partly due to its comorbidity with cardiovascular disease and suicide (>1,500/year). Approximately 1 in 4 women and 1 in 7 men are affected during their lifetime. The European Commission/Brain Council report (2011) has highlighted the growing seriousness of the problem, more people are living longer and the frequency of depression increases with age. Kungl. The Royal Swedish Academy of Sciences (2011) estimates the costs of mental illness "at least SEK 75 billion per year" and points out that "the allocation to psychiatric research corresponds to no more than 0.1-0.2% of the total cost of mental illnesses, while cancer research receives 2% of the costs of cancer diseases". The causes of depression are only partially understood and no new treatments have been developed since the 1950s. 25-35% of patients on standard antidepressants respond only partially or not at all. Thus, there is a great need to develop drugs based on new therapeutic principles. We and other researchers have found that a body substance, neuropeptide Y (NPY), is lowered in the brains and tissues of depressed patients and that successful treatment raises NPY. Similar results have been obtained in animal models. Taking these facts into account, we want to give NPY to depressed patients in a double-blind study and test its antidepressant effects. Our work is supported by the Swedish Research Council and may open new ways to treat recurrent depression.