When working together on a common document, collaborators frequently share and discuss their ideas about further revisions. Collaborative writing might, therefore, be thought of as a process of negotiating what changes to make among co-authors. The World Wide Web is an easily accessible infrastructure to facilitate such a communication process over documents. This paper explores the dialogues formed by comments exchanged among co-authors in a Web-based collaboration tool, Col*laboraci? A case study was performed where a small group of writers discussed and revised a common document, using this system. In the paper, I demonstrate how these dialogues are structured and what properties they have in relation to the context of collaborative reviewing processes. The analysis of dialogues is also used to reflect on design issues with regard to dialogue support and comment categorization.