During a period of 1969-1979 a total of 3174 small wild rodents of the genus Muridae and Microtinae (predominantly Microtus arvalis) were examined. The animals were trapped in five localities differing both in type of ecological conditions and epizootologic situation. Fox-rabies occurred here either enzootically, or epizootologically, or had been completely absent for many years in one of the localities investigated. Of the 71 isolated strains of RV 18 strains were isolated from brain, 25 from brown fat and 28 from salivary glands. Simultaneous isolation positivity in more than one tissue was sporadic. Virus isolations from deep-frozen material were mostly unsuccessful. Basic biological characteristics were determined in each isolate. The isolated strains differed in the rate of adaptation on albino mice and in intracerebral virulence. All isolates exhibited extraneural pathogenicity for common laboratory animals, dogs and foxes, showed distinct viscerotropism, stimulated formation of interferon and produced various forms of non-lethal infection. Incidence of "murine" rabies did not show any locality-specific differences and in longitudinally studied areas was enzootic. In a number of Czech districts there was observed a distinct relationship between fox-rabies incidence and the density of small game animal populations. Role of small wild rodents in the epizootology and epidemiology of rabies is discussed.