Bats are creatures of the night that are commonly held in fear. At first glance, those fears might seem to have some medical justification. Long known as vectors for rabies, it is now thought that bats may be the origin of some of the most deadly emerging viruses, including SARS. From research with other viruses, virologist Linfa Wang of the Australian Animal Health Laboratory knew bats could get chronic infections from viruses while not getting sick, making them ideal carriers for disease. Bats, civets and a menagerie of other animals were often found caged near one another in live-animal markets in Asia. So Wang hypothesized that bats might harbour SARS as well. Wang and his colleagues analyzed blood, throat and faecal swabs from 408 wild bats from China. Genetic analysis revealed five bats, which represented three of nine species of horseshoe bats tested, possessed viruses closely related to SARS. They reported last September that the genetic variation within those coronaviruses was far greater than that seen in human or civet SARS. Therefore, bats, probably having lived longer with the diseases, may be the origin of the coronaviruses seen in other species.