Environmental pollution has received considerable coverage in the news media. This has stimulated public interest and generated pressure on private industries and governmental agencies to take corrective action. Because the environmental issues have at times been presented in a simplistic and sensational manner, the corrective response by regulatory agencies and industry is often cursory and narrow. An approach, using biomarkers (biological responses), for assessing the biological and ecological significance of contaminants present in the environment is described. Living organisms integrate exposure to contaminants in their environment and respond in some measurable and predictable way. Responses are observed at several levels of biological organization from the biomolecular level, where pollutants can cause damage to critical cellular macromolecules and elicit defensive strategies such as detoxication and repair mechanisms, to the organismal level, where severe disturbances are manifested as impairment in growth, reproduction, developmental abnormalities, or decreased survival. Biomarkers can provide, not only evidence of exposure to a broad spectrum of anthropogenic chemicals, but also a temporally-integrated measure of bioavailable contaminant levels. A suite of biomarkers are evaluated over time to determine the magnitude of the problem and possible consequences. Pragmatically, the biomarker approach will help to assess the health of the environment, and, in addition, will enable scientists to defend the advice they provide concerning environmental issues.