Narrow reading has the potential to reduce vocabulary load and to provide rich opportunities for developing collocation knowledge, but these benefits rely on narrow reading increasing lexical repetition within a text. Hence, interest in narrow reading has been limited by the relatively small lexical effect of narrowing reading by topic (Nation, 2013). Nevertheless, research in data-driven learning and teaching and language corpora has reported positively on learners using concordances in a manner comparable to narrow reading. However, the potential for concordances to provide an increased lexical-repetition effect has not been assessed. This study bridges this gap by exploring the degree of lexical repetition available in concordances and identifies corpus composition as a key predictor of lexical repetition. The study uses standardised type-token ratio (sTTR) to analyse concordances extracted from corpora at three different levels of homogeneity/heterogeneity. The results show large, reliable variations in lexical repetition resulting from variation in corpus homogeneity/heterogeneity, and so identifies concordance-based narrow reading as a possible means of overcoming the limitations of traditional narrow reading by topic. The results are discussed with reference to pedagogical implications for language learners, teachers, and researchers.