Increasing awareness of the nature and extent of soil pollution on soil biota and their role in soil processes has resulted in exploring the possibilities of biological assessment systems to indicate the ecological condition of soils and to predict the ecological efficacy of e.g. policy measures. The research presented in this thesis is part of a project in which the possibilities of nematodes as bioindicator organisms are studied. The objectives of the study were to investigate i. the use of the nematode fauna to assess soil quality, and ii. the prospect of the nematode fauna to contributing to an ecological soil classification which can serve as a reference to assess soil quality. An ecological soil classification is based on a description of soils consisting of a set of both biotic and abiotic parameters.Besides the effects of certain pesticides on the occurrence of nematodes, many studies within the last decades showed changes in the composition of the nematode fauna due to e.g. heavy metals and other pollutants, fertilization and acidification. To assess soil quality by means of analyzing the composition of the nematode fauna, an effective and reliable instrument is needed. In Chapter 2 an assessment method based on life strategies of nematodes is described. Nematode taxa. can be classified from colonisers (r-strategists in the loose sense) to persisters (K-strategists sensu lato ) on a c-p scale. This c-p scale was divided into three classes, and of any soil sample the proportion of the nematode fauna belonging to each of these three classes was calculated. C-P triangles were used to visualize the distribution of the three c-p classes within a sample. It was shown that c-p triangles could be used to describe patterns in the composition of the nematode fauna which were found to be related to certain disturbances such as acute toxic compounds (arrow 2 Fig. 2.4) or those resulting in an increased availability of easily decomposable organic compounds (arrow 1 Fig. 2.4).In Chapter 3, c-p triangles were applied ...