Traditionally, assessments of ecological risks of soil pollution are based on chemical analyses compared to a set of standards. Recently, in the Netherlands, investigations were initiated to explore the possibility of including biological indicators in ecological risk assessment procedures. Nematodes are among the soil fauna groups that have promising characteristics as indicators for soil quality (i.e., ubiquitous,high species diversity, sensitive to various kinds of soil disturbances, speci¿ c nematode-based indicators). However, interpretation depends on comparison with undisturbed controls or references. As local reference sites or data are often unavailable, there is demand for a nation-wide reference system. In the present project, we built a database (DAWACO Nematodes) of 1600 nematode fauna samples from which all taxa were identi- ¿ ed. The samples were collected across the country, representing a variety of soil-, vegetation- and land-use types between 1985 and 2001. Samples from undisturbedor reference locations were analysed with multivariate analyses techniques to select clusters of samples (14 from terrestrial soils, six from aquatic sediments) with similar nematode fauna and habitat characteristics. Based on the statistical characterisation of the composition of taxa from a reference cluster, the probability of membership of any sample requiring assessment can now be calculated and evaluated.