Hemorrhagic fever with renal syndrome (HFRS) came dramatically to the attention of Western medicine in 1951 with the "new" disease becoming a major source of morbidity and mortality in American troops in Korea. Known there as epidemic hemorrhagic fever (EHF) or Korean hemorrhagic fever (KHF), it became apparent that it was the same disease as the endemic (epidemic) hemorrhagic nephroso-nephritis of the Soviet Far East and Songo fever of the Japanese Army in Manchuria. The conjecture that the milder epidemic (endemic) nephropathy of Scandinavia and European Russia was the same or a related disease has now been substantiated with the demonstration of close serological relationship of the Bunyamwera-like virus causing KHF (Hantaan virus) to that of HFRS in Finland, Sweden, European Russia, Greece and Yugoslavia. In the past decade the disease has been recognized as a serious problem in 19 provinces of China and in Japan, where the virus is the Hantaan virus. The severe EHF (or KHF) has its silent reservoir in the wild mouse Apodemus agrarius or in laboratory rats while the less virulent European disease resides in the voles Clethrionomys sp. A mild nonhemorrhagic form of the East Asian nephropathy is carried to man by infected urban rats, Rattus rattus or Rattus norvegicus, in Japan and Korea. All forms are carried to man as a respiratory infection "when a mouse (or rat or vole) coughs". Antibodies to the Hantaan virus have been found in man in India, Iran, Central Africa, Alaska, Bolivia and in wild rodents and urban rats in the USA where human cases of muroid virus nephropathy have not been recognized. Antibody patterns to Hantaan virus and to Scandinavian nephropathia epidemica virus antigens found in human and rodent sera in America and in Sweden, Yugoslavia, and European Russia suggest the possibility of yet a third (or more) virus serotype(s), and also the possible presence of the East Asian type of virus in Europe.