Theoretical models of marketing ethics propose that people first must perceive the presence of an ethical issue before the process of ethical decision making can begin. Through the concept of ethical sensitivity, the authors explore why some marketing researchers and not others recognize and ascribe importance to the ethical content in their decision situations. The authors examine two rival definitions of ethical sensitivity and develop a measurement procedure capable of discriminating between them. The procedure then is tested on two populations (marketing students and marketing research practitioners), and several determinants of ethical sensitivity are investigated. Results indicate that the two definitions of ethical sensitivity are empirically equivalent. Furthermore, results show that the ethical sensitivity of marketing researchers is a positive function of organizational socialization and perspective taking, but a negative function of relativism and formal training in ethics.