VTK (The Visualization Toolkit) has become one of the most popular modular visualization environments. It is an open source software, which has evolved rapidly, new tools being constinuously integrated and a new (minor) release being produced daily. This rapid evolution makes it difficult to develop a graphic user interface (GUI) while maintaining software integrity, that is coherence between interface and code. In this case traditionnal GUI production tools, such as application builders, are not appropriate. This paper proposes a re-engineering approach for automatically generating GUIs for VTK and gives solutions for most of the issues that have to be addressed. We take advantage of the object-oriented feature of VTK to propose a source code analysis method that generates a software components database. Then the rich information contained in this database is used to build a GUI for VTK using a specific GUI technology. This involves a fine analysis of the components of the VTK source and the relationships between them in order to select the components that should be included in the GUI. Then the GUI is generated, which includes a run-time environment to generate and execute the code corresponding to the applications designed by the users. Although VTK has been used to implement our software, the concepts and solutions proposed in this paper are general and could be applied to any object-oriented visualization toolkit.