This paper proposes a IS (Information System) design method based on the analysis of the system's organizational impact. Three organizational aspects are considered: (i) the analysis of decisional requirements of managers, (ii) the changes the DSS causes in users work habits and (iii) the changes the IS causes in organizational power equilibrium. Whereas points (i) and (ii) can follow existing literature, for the political changes problem instead, the paper proposes a new method based on the analysis of the network of relations existing in the organization. The analysis of organizational relations overcomes some of the limits of the classical organizational perspectives to political analysis of IS introduction. Moreover the paper presents an application of the proposed method regarding a service in a pubblic health agency, in which the relational approach to organizational analysis gives good results.