The new regional project in the fen grasslands around Nieuwkoop (province South Holland) is designed to provide a better habitat for butterfly species. Before a management plan can be set up, a detailed survey must be made of landscape elements in the region, the occurrence of nectar and food plants, and also of the butterfly species observed there. In 1990 data were collected by the Dutch Butterfly Foundation and used to set up a plan for the preservation and restoration of the butterfly population. The results of the survey are given, together with management recommendations of the Dutch Butterfly Foundation for the region.