While Reston and Lloviu viruses have never been associated with human disease, the other filoviruses cause outbreaks of hemorrhagic fever characterised by person-to-person transmission and high case fatality ratios. Cumulative evidence suggests that bats are the most likely reservoir hosts of the filoviruses. Ecological investigations following Marburg virus disease outbreaks associated with entry into caves inhabited by Rousettus aegyptiacus bats led to the identification of this bat species as the natural reservoir host of the marburgviruses. Experimental infection of R. aegyptiacus with Marburg virus has provided insight into the natural history of filovirus infection in bats that may help guide the search for the reservoir hosts of the ebolaviruses.