Lungs of 3159 animals of the forest complex from 90 areas of 30 administrative districts of Tyumen Province were examined by enzyme immunoassays for antigen of hemorrhagic fever with renal syndrome (HFRS) during 5 years, 1985-1989. The antigen of HERS virus was detected in the lungs of mammals of 8 species: Clethrionomys glareolus and Cl. rutilus, Siberian and Arctic lemmings (first findings in the world), M. oeconomus, field mouse, common and pygmy shrews. Nearly all the findings refer to the subzone of southern taiga and adjacent areas of subtaiga subzone where Cl. glareolus is the main reservoir of infection and Cl. rutilus an additional one. In the tundra zone, Siberian lemming is the main reservoir of infection and Arctic lemming an additional one. No natural foci of HFRS were found in forest steppe and forest tundra zones. In the subzone of the northern and middle taiga, the antigen was found only on 4 occasions: 3 in common shrews and one in Cl. glareolus (near the town of Khanty-Mansisk). An irregular annual infection rate with HFRS virus was observed in Cl. glareolus as well as its decline from spring to autumn. It cannot be ruled out that lemmings are carriers of a distinct HFRS virus serotype.