Fil: Enria, Delia. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Virales Humanas; Argentina.Fil: Pinheiro, F. Communicable Disease Program, Pan American Health Organization/World Health Organization, Washington, DC (FP); Estados Unidos.Hantaviruses and arenaviruses are naturally occurring viruses of rodents. Four South American hemorrhagic fevers caused by arenaviruses have emerged in the last 5 decades. All have similar clinical manifestations, with a case-fatality rate as high as 15% to 30%. Hantavirus infections have been increasingly recognized in South America since the description in 1993 of Hantavirus pulmonary syndrome. Given the diversity of rodent species in the region, it can be foreseen that many other viruses will be discovered, and some of them will be causing human illnesses of high public health impact.