Effective environmental management requires knowledge of the fate of contaminants in natural systems. Often these contaminants are anthropogenic in origin and are present in low concentrations. An important consideration is whether these substances will have an adverse biological impact on the biota present. Unfortunately, under these circumstances a long latent period frequently exists between initial exposure and the subsequent expression of a pathological state. An approach that can help document the exposure of a living organism to contaminants and possibly indicate the potential for deleterious impact is biological monitoring. This technique makes use of biological endpoints in living organisms that are indicators (biomarkers) of environmental insults. The organism functions as an integrator of exposure, accounting for abiotic and physiological factors that modulate the dose of toxicant taken up from the environment. The subsequent magnitude of the response can then be used to estimate the severity of exposure, hopefully in time to take preventive or remedial measures. Monitoring organismal responses as a means of evaluating exposure and effect of contaminants is a recognized concept for use in environmental health research. 1