This article describes an exploratory case study of secondary school physics teachers' conceptions of scientific evidence. The nature of teachers' conceptions of evidence was derived from an analysis of data collected from 1 preservice and 2 in-service teachers. Each teacher responded to a series of research prompts in multiple interviews and handwritten tasks. In these research prompts, the teachers thought aloud while designing experiments and critically evaluating student-collected data as presented in hypothetical classroom scenarios. Spoken and written data were recorded. The data set was coded and analyzed using standard qualitative analysis techniques. Data from this study suggest that, while contemplating the reliability and validity of hypothetical student-generated scientific evidence, the teachers frequently intertwined conceptions of evidence with subject matter concepts centrally relevant to the hypothetical investigation. Data also indicate that the relationship between subject matter knowledge and conceptions of evidence was more pronounced for some conceptions of evidence than for others. Results suggest that a fuller study is warranted. Suggestions for future research include exploring such relationships in other physics content areas as well as other scientific disciplines. Implications for science teacher education suggest that science and science methods courses should encourage preservice teachers to engage in original scientific research, as well as participate in peer review and critique. (Contains 2 figures and 1 table.)