We present initial results from a research project aiming at investigating how pupils and teachers develop interest and knowledge in science when working with socio-scientific issues (SSI). The theoretical framework developed for modelling and analysing authentic socio-scientific cases has been submitted to the conference (Ekborg et al.). So far, research concerning work with SSI has not particularly discussed the characteristics of the content of the issues. We need more detailed knowledge about what features in content and organization of the SSI that affect the development of interest, knowledge and self-efficacy among the pupils. The socio-scientific cases developed and used in this project are relevant according to characteristics of SSI described by Ratcliffe & Grace (2003) and to the national curriculum. During the autumn 2007 approximately 2000 pupils in Sweden have worked with one or several ases. A questionnaire-based instrument was used to measure the affective domain of students’ attitudes towards and interest in science. The students were asked to answer one questionnaire before starting to work with the first case and a second questionnaire after finishing a case. The theoretical base for development of the instrument and a description of how we will consider the multivariate characteristics of student and the situation (and in later stages of the research project - the learning outcomes) has also be en submitted to the conference (Lindahl & Winberg,). On the poster the first preliminary results of which components of the tasks are most influential on students’ interest to work with socio-scientific issues in secondary school will be presented. How do the task characteristics relate to students’ affective and cognitive experiences during the work with the cases? Will e.g. the context influence boys and girls differently?