Trans disciplinary research has positive connotations, but it is seldom discussed where and how in a research process trans-disciplinarity actually works. We reflect over two initiatives to gain advantages from different competences in a trans-disciplinary project. The first initiative concerned methodological collaboration and was successful. The second aimed to initiate a discussion on social science modes of analysis. This initiative was a disaster. We conclude that it is important not to have naive expectations of trans disciplinary research since it raises issues of theory of science, ethics, validity and integrity.