The phrase "virtual community" is often used to describe long term computer-mediated conversations amongst large groups. This paper suggests that such conversations may be better viewed as instances of a participatory genre, rather than as community. A genre-oriented analysis is useful because it encourages a focus on the medium within which the discourse is embodied. As an example we analyze an on-line conversation from the perspective of genre: we identify its communicative purpose, regularities of form and substance (such as word play and affirmation), and the situation which gives rise to these regularities. We then examine ways in which the discourse medium supports these regularities and enables participants to establish and reinforce the conversation's underlying conventions. More generally, we believe that genre-oriented analyses such as this can play an important role in the design of participatory media.