An outbreak of Hantavirus Pulmonary Syndrome (HPS) occurred in the western U.S. in 1993. This outbreak was surprising because serious disease due to hantavirus had not been reported previously in the U.S., and hantavirus had not been documented to cause significant pulmonary disease. Epidemiologic investigation discovered a novel strain of hantavirus as the etiologic agent of HPS. The Centers for Disease Control (CDC) proposed the name of Muerto Canyon virus for this novel hantavirus, which is transmitted through aerosolized excreta of infected rodents. HPS begins with a prodrome of fever, myalgia, and respiratory symptoms followed by the acute onset of respiratory distress. Since HPS has a mortality of 60%, early recognition is important so that supportive treatment can be initiated promptly. Intravenous ribavirin is investigational therapy and can be obtained through the CDC in Atlanta.