This article examines the management of participation in calls to radio phone-in programmes. In the broadcast media, there are increasing occasions for interaction between 'professionals' and lay members of the public, particularly within what have come to be known generically as public participation programmes (talk shows, phone-in programmes and the like). People call in to phone-in programmes for various reasons; to give opinions, to get advice, and often to ask questions. In the particular phone-ins analysed here, callers are invited to put questions to leading politicians of the day about their election policies. In many institutional contexts for talk (e.g. courtrooms, classrooms, political interviews) the role of questioner has been found to be a more powerful interactional position than the role of answerer. Through an analysis of the organization of the phone-in calls, this article argues that the potentially powerful discourse role of questioner is interactionally 'defused' through the participatory framework of the call. The author shows how the mediated interactional structure of these calls limits the range of possible actions available to callers in their institutional position as questioners, and thus produces constraints on what callers can actually achieve in this particular context for institutional talk.