Abstract. Internet technology holds significant potential to respond to business, educational, and social needs, but this same technology poses fundamentally new challenges for research ethics. To reason about ethical questions, researchers and ethics review boards typically rely on dichotomies like "public" versus "private," "published" vs. "unpublished," and "anonymous" vs. "identified." However, online, these categories are blurred, and the underlying concepts require reinterpretation. How then are we to reason about ethical dilemmas about research on the Internet? To date, most work in this area has been grounded in a combination of theoretical analysis and experience gained by people in the course of conducting Internet research. In these studies, ethical insight was a welcome byproduct of research aimed primarily at exploring other ends. However, little work has used experimental methods for the primary purpose of contributing to our reasoning about the ethics of research online. In this paper, we discuss the role of empirical data in helping us answer questions about Internet research ethics. As an example, we review results of one study in which we gauged participant expectations of privacy in public chatrooms (Hudson & Bruckman, 2004b). Using an experimental approach, we demonstrate how participants' expectations of privacy conflict with the reality of these public chatrooms. Although these empirical data cannot provide concrete answers, we show how they influence our reasoning about the ethical issues of obtaining informed consent.