The Research Institute for Nature Management (R.I.N.) has compiled all available information on the distribution of bats in the Netherlands up till 1968. The data were derived from literature and museum specimens, as well as from numerous unpublished observations. Around 1960 much was known already on the winter dwellings of various species of bats, especially those in marl pits and fortresses. Less details were available concerning the distribution of bats in summer. Only one species, Nyctalus noctula, had been studied during the summer. During the past ten years valuable information on hibernacula could be added by continued research in marl pits and fortresses, and by investigations in cellars of castles and in former ice cellars. Besides, Dutch investigators started to pay attention to summer resorts of bats in towers and on lofts of churches, castles and other old buildings. From 1961 to 1969 about 1320 buildings have been inspected.