This paper presents a review of biologic mechanisms of stress and analyzes their role in the pathogenesis of depressive disorder. Recent investigations point to the fact that apart from hereditary predisposition in the pathogenesis of depression different biologic mechanisms, included into the regulation of organism response to stress, have an important role. These findings are in harmony with the well known fact from the clinical practice, that exposure to stressor may lead to depression in persons who do not normally react depressively. The newest findings point out the significance of biologic mechanisms of stress which exert influence on a person at the early neonatal period, even before that, during the embryonal development. However, on the other hand in humans it is very probable that mechanisms, included into the regulation of response of the organism to stress, are important for the homeostasis of emotions and willing--instinctive dynamisms, and indirectly for the cognitive functions, as well as for maintaining harmony among these dimensions of psychic existence and demands of the external--physical, biologic and social--environment.