Medical co-morbidity is considered to be one of the reasons of chronicity or treatment resistance in depression. Solving the other problem may result in improvement of depression. Metabolic disorders constitute an example for this phenomenon. Disturbances of the electrolyte metabolism, especially magnesium deficiency is reported to have caused a wide range of psychiatric disorders, from dysphoria to psychosis. We found out that two of our patients with a diagnosis of depression resistant to treatment had hypomagnesemia after routine laboratory tests. Following a course of magnesium replacement therapy, we observed that the depressive states of the patiens improwed markedly. In this paper we present these two cases.