Secondary transmission of Ebola virus infection in humans is known to be caused by direct contact with infected patients or body fluids. We report transmission of Ebola virus (Zaire strain) to two of three control rhesus monkeys (Macaca mulatta) that did not have direct contact with experimentally inoculated monkeys held in the same room. The two control monkeys died from Ebola virus infections at 10 and 11 days after the last experimentally inoculated monkey had died. The most likely route of infection of the control monkeys was aerosol, oral or conjunctival exposure to virus-laden droplets secreted or excreted from the experimentally inoculated monkeys. These observations suggest approaches to the study of routes of transmission to and among humans.