this article analyses iso9000 normalization processes as sources of organizational isomorphism according to the new institutional theory. we present two in-depth case studies in the french computer industry showing that there are two manners to implement iso9000 standards: an in-depth procedure (concerned with organizational effectiveness and with external legitimacy) and an instrumental one (only concerned with external legitimacy). our findings show that resistance to change is a common phenomenon in iso9000 implementation programs having high impact on organizational power games and informal structures. in order to face these issues we suggest that consultants must go beyond engineering consultation methods that are only concerned with the structural fit between the organizational standards and the iso9000 requirements. the paradox hrm model shows that information that threatens an organization's collective self-concept is often ignored, rejected, reinterpreted or hidden. the manifestation of social defenses - the ways of groups of people deal with non-contained forms of anxiety and fear, can be seen as sources of behaviors blocking organizational change.