In a mountainous area in the Dinaric Beech-Fir Forest of southern Slovenia, summer nests of the European fat dormouse (Glis glis) were collected. From these dormouse nests, 180 Monopsyllus sciurorum sciurorum fleas were examined by polymerase chain reaction with primers for the Rickettsia citrate synthase gene. Samples from one nest yielded the expected 381 base pair DNA product. The origin of the DNA product was identified as Rickettsia typhi by AluI restriction fragment length polymorphism analysis. Inoculation of the triturated positive fleas into Vero cell culture resulted in the cultivation of a rickettsia which reacted with polyclonal and species-specific monoclonal antibodies for R. typhi. The widespread distribution of this sylvatic flea species in nearly all of Europe as well as in the Middle East and its presence on other mammalian and avian hosts suggests that R. typhi might exist in unrecognised enzootic cycles. Further investigations are needed to determine the extent of these cycles in Europe and the potential occurrence of human infections.