English plays an increasingly important role at Swedish universities but not much is known about its effects on the quality of teaching and learning. Therefore, a large research project which is collaborative and interdisciplinary, crossing language studies in humanities with education, is being planned. One of several aims of the project is to study the consequences of teaching in English on learning and study achievements. A few pre-studies have been carried out in order to developmore detailed research questions. Two of the pre-studies will be presented in this paper. In one of them, ten university teachers with Swedish as their native language have been interviewed about their experiences and perceptions of strategies, problems and consequences of teaching in English. Five of the interviewees had no experience of teaching in English and five had experience. A result was that the teachers with no experience of teaching in English seemed to anticipate and fear lower quality in their teaching. This assumption was confirmed by the teachers who had experience of teaching in English. They found it difficult to explain and talk about complicated issues in a profound way and also to use humour. Another problem concerned the big differences in international students‘ knowledge of English and cultural differences. In the other pre-study, observations have been conducted in lectures, seminars and group-work sessions of a course in social sciences given in English. The results of the latter study indicated that the apprehension ofthe contents may be inflated among students who have Swedish as their native language. Furthermore, there was empirical support that their skills in both English and their native language were influenced. A conclusion is that the pilot studies confirmed that there is a great need for further research on the effects of teaching in English at Swedish universities.