AbstractThe purpose of this study was to investigate the relationships between students' conceptions of the nature of science and their reactions to evidence that challenged their beliefs about socioscientific issues. This study involved 41 pairs of students representing “critical cases” of contrasting ethical viewpoints. These 82 students were identified from a larger sample of 248 students from 9th and 10th grade general science classes, 11th and 12th grade honors biology, honors science, and physics classes, and upper‐level college preservice science education classes. Students responded to questions aimed at revealing their epistemological views of the nature of science and their belief convictions on a selected socioscientific issue. The smaller subset of students was selected based on varying degrees of belief convictions about the socioscientific issues and the selected students were then paired to discuss their reasoning related to the issue while being exposed to anomalous data and information from each other and in response to epistemological probes of an interviewer. Taxonomic categories of students' conceptions of the nature of science were derived from the researchers' analysis of student responses to interviews and questionnaires. In some instances, students' conceptions of the nature of science were reflected in their reasoning on a moral and ethical issue. This study stimulated students to reflect on their own beliefs and defend their opinions. The findings suggest that the reactions of students to anomalous socioscientific data are varied and complex, with notable differences in the reasoning processes of high school students compared to college students. A deeper understanding of how students reason about the moral and ethical context of controversial socioscientific issues will allow science educators to incorporate teaching strategies aimed at developing students' reasoning skills in these crucial areas. © 2002 Wiley Periodicals, Inc. Sci Ed 86:343–367, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/sce.10025