Physiology faculty members at a wide range of institutions (2-yr colleges to medical schools) were surveyed to determine what core principles of physiology they want their students to understand. From the results of the first survey, 15 core principles were described. In a second survey, respondents were asked to rank order these 15 core principles and, independently, to identify the three most important for their students to understand. The five most important core principles were "cell membrane," "homeostasis," "cell-to-cell communications," "interdependence," and "flow down gradients." We then "unpacked" the flow down gradients core principle into the component ideas of which it is comprised. This unpacking was sent to respondents who were asked to identify the importance of each of the component ideas. Respondents strongly agreed with the importance of the component ideas we had identified. We will be using the responses to our surveys as we begin the development of a conceptual assessment of physiology instrument (i.e., a concept inventory). (Contains 7 tables.)