The paper seeks to demonstrate that, first, over the course of interaction in the radio phone-in events, participants display orientation to various aspects of their co-participants´ identities, second, since membership categories emerge and are developed at various sequentially relevant times, membership categorisation processes are closely tied with the event´s sequential organisation, and, third, categorisation bears on politeness aspects of interaction as the participation in the public ´arena´ causes participants´ faces to be constantly at stake. The methodological underpinnings of the paper represent the approaches of Membership Categorisation Analysis and the model of politeness based on the conceptualisation of face. The data are drawn from the corpus of Nočné dialógy (´Night Dialogues´) radio phone-ins broadcast on the Slovak public radio over the period of 1995-2004. The paper further attempts to demonstrate that participants are engaged in category work which sequentially unfolds in the course of the production of phone-in calls. Participants´ progressive involvement in talk is closely linked with the construction of ´layers´ of their categorial identities. The membership category of ´location´ represents the minimum agreed-upon canon of callers´ call-relevant identities. As the category is universally applicable, it bears the least face-threatening potential, for which reason it is used explicitely. In contrast, strategies of non-explicit categorisation, i.e. invoking categories through category-relevant predicates, apply to those topic-relevant categories which carry a significant face-threating ´load´ (e.g. ´family status´, ´political affiliation´, etc.). In summary, sequential organisation and category work are seen as being closely intertwined, with the latter also being employed as a positive and negative politeness strategy.