This study examines the verbal interactions among a group of pre-service teachers as they engaged in scientific discussions in a medicinal chemistry course. These discussions were part of the course that encompassed an explicit instruction of scientific argumentation structures as well as an applied component, whereby the pre-service teachers learned the content of medicinal chemistry through cases developed using the strategy of competing theories. By adopting a case study approach using sociocultural framework of learning, we examined the interactions between the pre-service teachers using video data. We describe 12 possible forms of interactions during discussions--(1) seeking clarification, (2) figuring out loud, (3) sharing information, (4) agreement, (5) asking questions, (6) providing explanations, (7) raising strategic and procedural issues, (8) stating claims, (9) disagreement, (10) sharing perspectives, (11) offering alternatives, and (12) persuasion. The pre-service teachers engaged in figuring out aloud and seeking clarifications frequently, and used persuasion least in their discussions. To clarify their ideas and thoughts, pre-service teachers commonly rebut their counterparts and used warrants to support their own assertions. A similar pattern was also observed when figuring their thoughts out loud. Our findings suggest that pre-service teachers were able to carry out rebuttals in the argumentation process. However, the quality and function of their rebuttals can be improved by deepening their understanding of the subject matter knowledge and the science argumentation structure. Implications are discussed.