Discussion forums are a central part of Web 2.0 and Enterprise 2.0 infrastructures. The health and sustainability of forums is dependent on the information exchange behaviour of its contributors, which is expressed through online conversation. The increasing popularity and importance of forums requires a better understanding and characterisation of communication behaviour so that forums can be better managed, new services delivered and opportunities and risks detected. In this paper, we present an empirical analysis of user communication roles in a medium-sized bulletin board and we analyse the composition of several forums in terms of these roles, demonstrating similarities between forums based on underlying user behaviour rather than topic. Copyright © 2010, Association for the Advancement of Artificial Intelligence (www.aaai.org). All rights reserved.