The science of ecotoxicology has made exciting advances during the past few years. Recent advances in the use of sensitive subcellular biomarkers, bioaccumulation and food web models, ultra-trace level detection of contaminants, and contaminant partitioning and bioavailability factors have allowed ecotoxicologists to better define contaminant exposures. These advances, when integrated with more traditional approaches (e.g. standardized laboratory toxicity testing, population/community structure characterization) can provide meaningful assessments of ecosystem perturbations. Despite these advances, there is still a limited understanding or application of the complex fate and effect interactions of multiple stressors and receptors in assessments of ecosystem contamination. This reality raises uncertainties which cannot be ignored when using traditional, short-term approaches of assessment. The integrated use of newer in situ assessments of multi-stressor exposures, coupled with more traditional laboratory and field methods reduces uncertainty and improves our ability to identify significant stressors.