Andes virus, associated with the native rat Oligoryzomys longicaudatus, causes hantavirus pulmonary syndrome (HPS) in the northern Patagonian regions of Argentina and Chile. Another hantavirus, Oran virus, also causes HPS and is apparently associated with the same rodent species in extreme northern Argentina. However, the rat populations appear to be disjunct and careful taxonomic and distributional studies would be required to determine if these rodent populations represent distinct species and to define the potential HPS-endemic areas associated with each virus.