Doctoral students in the natural sciences who are writing research for the first time and also writing in an additional language (L2) need to acquire knowledge of the genre of the research article (RA). This knowledge can be elusive. One instructional activity that can mediate genre knowledge is students acting as reviewers to peers' RA texts. However, mediation of genre knowledge is contingent on reviewers' focusing on genre features of peers' texts. To explore the focus of L2 doctoral students' peer review, this study examined online feedback provided by 24 L2 doctoral reviewers on 73 texts written by their L2 peers. To determine the potential relevance of the feedback to the scientific research article, review comments were thematically coded, and the categories of comments were then compared with descriptions of text features of RAs in the natural sciences. Findings showed that review comments focused on precision, organization, cohesion, voice and stance, and research knowledge, categories that reflect key aspects of scientific RAs.