This study investigates upper secondary school students’ argumentation and in- terdisciplinary integration of biology and chemistry in a virtual environment. Pre and post-tests (content knowledge, scientific reasoning) were carried out. Stu- dents (n=35) collaborated in small groups to generate hypotheses, study plans and presentations which were analysed by SOLO taxonomy and videotaped spoken products were presented. Results of this qualitative study showed that the students were able to generate hypotheses despite the non-supportive cur- riculum and were able to integrate biological and chemical concepts and spon- taneously argue in virtual environment. The results are discussed with respect to collaborative argumentation and interdisciplinary integration.