In the midst of the recent Ebola outbreak, scientific developments involving infection challenge experiments on nonhuman primates (NHPs) sparked hope that successful treatments and vaccines may soon become available. Yet these studies pose a stark ethical quandary. On the one hand, they represent an important step in developing novel therapies and vaccines for Ebola and the Marburg virus, with the potential to save thousands of human lives and to protect whole communities from devastation; on the other hand, they intentionally expose (...) sophisticated animals to severe suffering and a high risk of death. Other studies that infect NHPs with a lethal disease in order to test interventions that may prove beneficial for humans pose the same ethical difficulty. Some advocates have argued that all research on primates should be phased out, and ethicists have questioned whether a moral justification of primate research is possible. A 2010 European Union directive banned virtually all research on great apes, and 2013 guidelines from the National Institutes of Health (NIH), based upon recommendations in an influential 2011 Institute of Medicine (IOM) report, eliminated most biomedical research with chimpanzees in the United States. But studies involving other NHPs face no comparable restrictions.Should research on NHPs other than great apes be subject to tighter restrictions than it currently is? In this article, we explore this general question in the context of one particular type of biomedical research: infection challenge studies. We advocate a presumptive prohibition on infection challenge experiments in NHPs, but we also argue that exceptions to this prohibition are permissible, subject to strict substantive and procedural safeguards, when necessary to avert substantial loss of human life or severe morbidity for a substantial number of people. (shrink)