In different habitats around Saarbrücken, all fox dens were searched systematically and their use by foxes checked regularly. Most of the dens used were not dug by the foxes themselves. In the wooded sandstone areas, den sites are plentiful, allowing the foxes a wide choice. In the agricultural limestone area, dens are restricted to a few suitable places. During the breeding season, foxes spent their inactive periods mainly inside the dens. At other times, dens seemed to have mainly social functions. The distribution of foxes can be heavily influenced by the distribution of suitable dens. The influence of reducing foxes in dens by gassing and shooting on population dynamics is discussed. It is suggested that it can be a density-limiting mortality factor in areas with restricted den availability.