Anthropogenic pollutants may potentially adversely affect biodiversity in both terrestrial and aquatic ecosystems. Species, functional, and genetic diversity are the target biodiversity aspects for research on the impact of toxicants. In this article we present examples of studies conducted on this subject and attempt to draw conclusions on both the effects themselves and the most promising ways to study them. Although a number of studies show that pollutants affect diversity in a number of ways, as reflected in changes in species richness or evenness as well as in genetic and functional diversity, some researchers report no effects or even effects contradictory to prescience.