This study sought to develop a method for describing readers' perceptions of the topical organization of prose and to specify text features that determine perception of organization. A hierarchical clustering analysis was applied to high-school and college readers' judgments of the topical relatedness of sentences in two prose passages. This produced semantically similar clusters of sentences that were reliable indicators of topical organization. In searching for text features related to topicality, it was found that the perception of topicality was weakly related to the lexical similarity of sentences and that both the spatial relationship between sentences and typographical conventions influenced the perception of topicality. (Author/AA)