This paper examines a section of the Multimodal Academic Spoken Corpus (MASC), which contains the video recording and transcription of the presentations and subsequent discussion sessions that took place at a specialized international conference on chemistry held at the Universitat Jaume I. The study focuses on the subcorpus of discussion sessions. The relationship between the participants is the point of departure in the analysis of interaction. The macrostructure of the discussion session is also studied to identify the chairs' discursive functions. Finally, a closer multimodal analysis of the chairs' turns is conducted, which provides insight into how the discussion unfolds with the chairs' participation.