Section 121 of the amendments (1986) to the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (SUPERFUND) calls for hazardous waste site remediations that will permanently and significantly reduce the volume, toxicity, or mobility of hazardous substances, pollutants, and contaminants. Traditional engineering technology has concentrated on reduction in volume and mobility as assessed by chemical and geophysical measures, assuming that reduction in volume and mobility would lead to reductions in toxicity. Environmental scientists long have argued that this might not be the case. However, lack of consensus on how complex hazardous waste mixtures should be measured toxicologically has hampered integrated assessments. Therefore, new work was initiated to assemble a battery of aquatic and terrestrial bioassays to be evaluated comparatively against several individual chemicals, mixtures of chemicals, and actual waste site chemical mixtures. The bioassays were then applied to a mobility reduction demonstration to help assess its overall chemical, physical, and biological performance. Results indicated that although remediation accomplished the primary objective of mobility reduction, it introduced undesirable secondary effects (toxicity). These trade-offs must be considered in the holistic sense with regard to the implementation and evaluation of remediation measures.