Abstract
The discovery that bats are the reservoir hosts of the coronavirus that causes SARS in humans raises important questions about how we monitor and control emergent disease outbreaks. In his Perspective, [Dobson][1] focuses on the need to know more about the distribution of pathogens in their natural reservoir hosts and asks whether the absence of pathology that characterizes these relationships may reflect subtle differences in the immune responses of bats. [1]: http://www.sciencemag.org/cgi/content/full/310/5748/628