What science-related knowledge is actually used by nurses in their day-to-day clinical reasoning when attending patients? The study investigated the knowledge-in-use of six acute-care nurses in a hospital surgical unit. It was found that the nurses mainly drew upon their professional knowledge of nursing and upon their procedural understanding that included a common core of "concepts of evidence" (concepts implicitly applied to the evaluation of data and the evaluation of evidence--the focus of this research). This core included validity triangulation, normalcy range, accuracy, and a general predilection for direct sensual access to a phenomenon over indirect machine-managed access. A cluster of emotion-related concepts of evidence (e.g. cultural sensitivity) was also discovered. These results add to a compendium of concepts of evidence published in the literature. Only a small proportion of nurses (one of the six nurses in the study) used canonical science content in their clinical reasoning, a result consistent with other research. This study also confirms earlier research on employees in science-rich workplaces in general, and on professional development programs for nurses specifically: canonical science content found in a typical science curriculum (e.g. high school physics) does not appear relevant to many nurses' knowledge-in-use. These findings support a curriculum policy that gives emphasis to students learning how to learn science content "as required" by an authentic everyday or workplace context, and to students learning concepts of evidence.