Exposure of an organism to a genotoxic chemical may result in the formation of covalently bound adducts between the chemical (or its metabolites) and the DNA; faulty repair of these adducts often results in mutations and, sometimes, cytogenetic changes. The primary effects of such exposure (i.e. adduct formation) and the subsequent effects on the DNA (mutation, cytogenetic damage) may be monitored using a number of assays of varying sensitivity and specificity. Recent developments in molecular biology offer new possibilities for detecting DNA damage. In this laboratory DNA fingerprinting by arbitrarily primed polymerase chain reaction (AP-PCR) was investigated in order to establish whether it can reveal differences in the DNA fingerprints of animals exposed to benzo[a]pyrene in the laboratory and of animals from control and from polluted areas. The results indicate that differences between control and exposed animals were detectable; these results, together with those from other laboratories, indicate that DNA fingerprinting by AP-PCR offers a useful alternative biomarker assay for the detection of the genotoxic effects of environmental pollutants. This paper reviews the application of PCR based DNA fingerprinting procedures in mutation detection and discusses their application to ecotoxicological studies.