Lung tissues from 547 rodents and 26 insectivores captured between 1981 and 1984 in central Bosnia (Fojnica) and central Serbia (Cacak), 2 regions known to be endemic for hemorrhagic fever with renal syndrome (HFRS), were examined for hantaviral antigen by the indirect immunofluorescent antibody technique. Antigen was detected in 17/231 Apodemus flavicollis, 3/187 A. sylvaticus, 1/46 A. agrarius, 4/32 Mus musculus, and 3/28 Clethrionomys glareolus. In addition, antibodies against Hantaan and Puumala viruses were found in serum pooled from 2 C. glareolus captured in Fojnica and 6 Pitimys subterraneus caught in Cacak. Sera of 27 HFRS patients from different parts of Yugoslavia were tested against 3 serotypes of hantavirus. Patients from Bosnia and Serbia had highest titers against Hantaan virus, while patients from Croatia had highest titers against Puumula virus, the agent of nephropathia epidemica.