Depression is considered as a chronic and recurring illness with functional impairment, significant disability, morbidity and mortality. Despite the extensive research carried out on depression, its pathophysiology is still poorly understood. An important problem concerning research into depressive disorder is the lack of biological markers which could improve diagnosis or indicate a risk of developing depression or risk of relapse. Several reports indicated decreased zinc concentrations and even its deficit in clinical depression, so the measurement of the concentration of this element in the blood of patients was suggested as a useful and specific clinical marker of depression. The reported results indicated that the serum zinc level might be a marker of depression as a state (state marker) in treatment responsive patients. However, in drug-resistant depression a decreased concentration of zinc may be a marker of traits (trait marker). It seems, however, that the measurement of the concentrations of zinc might be in the future a component of the battery of tests; of markers of immune activation and oxidative stress rather than itself alone.