Parasites are attracting increasing interest from parasite ecologists as potential indicators of environmental quality because of the variety of ways in which they respond to anthropogenic pollution. However, until recently, little was known about the accumulation of toxins within parasites. Certain parasites, particularly intestinal acanthocephalans and cestodes of fish, can accumulate heavy metals at concentrations that are orders of magnitude higher than those in the host tissues or the environment. In this review, Bernd Sures, Roy Siddall and Horst Taraschewski discuss the recently described phenomenon of conspicuous metal accumulation by parasites and how this might be applied to environmental monitoring. They also suggest how environmental science and parasitology might profit from each other in the near future.