This contribution aims to study the use of discourse markers in a French radio program called Inter-activ, by adopting the approach of interaction analysis. The interaction explored is a phone-in program in which telephoned questions and comments from listeners are broadcast and members of the public are given the possibility to have their saying on political issues. My analysis will particularly focus on the discourse markers used by participants in the co-construction of this specific communicative interaction. The analytical approach I followed relies mainly on that adopted by Bruxelles and Traverso (2001) in their description of the French discourse marker ben. To perform this type of study I analysed occurrences of markers and then concentrated on more general units, namely the type of phenomena related to interaction activities and participation framework. This paper focuses specifically on some units, particularly on alors and voilà. The purpose is to describe these markers, their meaning and their pragmatic functions in relation to broader interactional characteristics.