OBJECTIVE: to understand the changing roles of nurses in labor division organization in hospitals from the Manchester Triage System implementation in an emergency hospital. METHODS: this is an ethnographic study that used different production techniques and data analysis. RESULTS: the Manchester Triage System organized flows and places resulting in quality of care and changes in work processes. Conflict relationships related to disagreements in risk stratification were present. FINAL CONSIDERATIONS: the traditional roles of nurses have been transformed, but it cannot be said that there was a structural change in their position in labor division organization in hospitals. The frontiers of autonomy, therefore of increasing the professionalization of nurses, are neither fixed nor stable, expanding or contracting according to the micropolitical changes in the governance of care.