We tried to determine the reasoning behind the stances taken by a group of 19-21-year-old students on the controversial issue of the feasibility and acceptability of human gene therapy. The students were in training at a biotechnology institute. We organised classroom debates, punctuated by phases of epistemological "disturbances". We used a variety of resources from authentic genetic therapy cases. We also worked on the reconsideration of Crick's model on the basis of recent results in molecular genetics and genomics. We stimulated critical analysis by presenting texts on the failure of gene therapies. This also encouraged the students to evaluate the empirical evidence, in the light of current molecular biology data that challenges Crick's dogma. We observed an increase in the intensity of the argumentation. According to Habermas, in all the didactic situations forms of communicative action are used less frequently, whereas forms of strategic action are the most prevalent. However, we found that in the case of the final situation, the students' discourse was more in keeping with communicative action than in the other situations. (Contains 5 tables.)