Turn structure and timing are examined in a variety of quasi-synchronous computer-mediated interfaces. The message window size, presence of scrolling, a single message window vs. message windows for each participant, and message persistence were systematically varied for pairs of interlocutors engaged in the same decision-making task. Participants produced more total words and more turns in conditions with larger windows and in those with scrolling, while separate windows conditioned even larger increases on these measures. Turn sizes were smaller in the latter conditions and response times were faster. In the persistent separate-window conditions, messages from the partner intervened before participants completed responses in over half of the messages.