In Europe, Puumala (PUU) is a hantavirus responsible for a human disease called nephropathia epidemica and its natural reservoir is the red bank vole, (Clethrionomys glareolus). Although the population densities and the prevalence rates of infection were high in red bank voles in southern Belgium during the 1996 and 1999 epidemic years, the percentages of infected rodents were low in 1997 and 1998, when only a few positive sites were found. Antibodies against PUU virus were mainly detected in the red bank vole but also in the wood mouse (Apodemus sylvaticus) and the red fox (Vulpes vulpes). The analysis of genomic sequences has shown that the Belgian viruses and the German strain Erft constitute a genetic lineage well separated from the other European PUU strains.