The article focuses on the difficulties the epidemiological instrument faces when dealing wih questions posed by contemporary health problems, in which the concept of stress finds broad diffusion. Thus there is a discus-sion about the theoretical-concepual framework of the theory of stress and its developments. Besides, the text points out the limitation of the method and of the available epidemiological models when they talk about: 1 - manifesta-tions whose predicability cannot be delimited; 2 - phenomena placed in different hierarchic leveis. In such cases, the theorization underlying the noion of risk, used to explain sikliness at the individual levei proves to be insufficient. The complexity of the health'illness process demands another epistemological paradigm which allaws the subjec of the epidemiological research develop other ways of demarcating and understanding its object.