Numerous grounds have been offered for the view that healthcare workers have a duty to treat, including expressed consent, implied consent, special training, reciprocity (also called the social contract view), and professional oaths and codes. Quite often, however, these grounds are simply asserted without being adequately defended or without the defenses being critically evaluated. This essay aims to help remedy that problem by providing a critical examination of the strengths and weaknesses of each of these five grounds for asserting that (...) healthcare workers have a duty to treat, especially as that duty would arise in the context of an infectious disease pandemic. Ultimately, it argues that none of the defenses is currently sufficient to ground the kind of duty that would be needed in a pandemic. It concludes by sketching some practical recommendations in that regard. (shrink)