The goal of this case study is the development of a method to investigate in the metabolism of an urban region to supply a tool for environmental protection and resources conservation. As examples the materials carbon, nitrogen and lead are investigated. The "Material Flux Analysis" can be used for early recognition of future problems of environmental loading and resource depletion, to set priorities for and to define measures to protect the environment and to use resources more efficiently, to analyse and improve the effects of measures taken. The case study is a necessary step towards reaching the goal to assess and control the metabolism of the city of Vienna.