Epidemic hemorrhagic fever was known to exist in Korea for the first time in 1951 among soldiers of the United Nations during Korean War. Since that time it has been known as Korean hemorrhagic fever (KHF). In 1976 Lee and Lee successfully discovered an antigen in the lungs of Apodemus agrarius coreae which gave specific immunofluorescent reaction with convalescent sera from patients of KHF. In 1978, Lee et al. Isolated this antigen from blood of KHF patients and perfected a specific serological test for diagnosis of KHF. The aetiologic agent of KHF was identified as a new member of Bunya- viridae and was named Hantaan virus after the Hantaan river which runs near the 38th parallel between South and North Korea. A close aetiological relationship was established between KHF and hemorrhagic fever with renal syndrome in USSR, nephrophathia epidemica in Scandinavia and epidemic hemorrhagic fever in Cliina and in Japan. The working group on HFRS at a WHO meeting in Tokyo in February 1982 recommended that KHF-like diseases with different names in Euro-Asia continent should be referred to as Hemorrhagic fever with renal syndrome (HFRS). This report describes the difference between clinical diagnosis and specific serological diagnosis of HFRS. The indirect IF antibody technique was performed for serologic diagnosis of the patients having a symptom of HFRS from 1982 to 1984 and the results are summarized as follows. 1. Specific serological diagnosis of the 3571 cases of suspected HFRS clinically showed that about 50% was proven to be of definite HFRS. 2. Blined samples of 205 sera-from the hospitalized patients was used for the specific serological diagnosis of HFRS, 4 cases were diagnosed to be HFRS serologically and of which, 2 cases were diagnosed as HFRS clinically but 1 case, chronic renal failure, and the other, G-I bleeding. 3. Patients diagnosed as G-I bleeding and acute abdomen in early stage of HFRS should go through detailed specific serological diagnosis of HFRS since all of eight cases of such patients were expired after surgical operation.