What affects speakers' production of ambiguous utterances in dialogue? They might consider ease of production for themselves, or ease of comprehension for their addressees. Previous research has demonstrated that ease of production plays a role in speakers' syntactic choices, but that ease of comprehension does not. However, such studies have not employed dialogues that involve role swapping on a turn-by-turn basis. In our experiment, participants alternated in giving and following instructions to move objects around on a grid. They tended to repeat the syntactic form just used by their interlocutor, reflecting sensitivity to ease of production. More interestingly, they were more likely to disambiguate their utterances when the visual context was potentially ambiguous than when it was not, reflecting sensitivity to ease of comprehension. We conclude that speakers pay attention to their beliefs about their addressees' ease of comprehension, in addition to considering ease of production for themselves.