A summarization task was used to study whether headings influence readers' representations of the topic structure of a text. College students (Experiments 1-3) and sixth- and eighth-graders (Experiment 3) summarized a multiple topic text that (a) included headings introducing every new subtopic, (b) included headings introducing half of the new subtopics, or (c) included no headings. In all experiments, topics were more likely to be included in a summary if they were signaled than if they were not signaled. This effect was magnified when the text was only half signaled: Signaled topics were more likely to appear in a summary if only half the text topics were signaled than if all of the topics were signaled; however, unsignaled topics were less likely to appear in a summary if half of the text topics were signaled than if none of the text topics were signaled. The findings demonstrate that readers rely heavily on headings in a task that emphasizes attention to a text's topic structure. It is suggested that previously observed signaling effects on text recall are mediated by effects on how readers represent a text's topic structure. Copyright 2001 Academic Press.