The objective of a SETAC Pellston Workshop held in Portland, Oregon, USA, in November 2004 was to evaluate the use of field-based biological effects and exposure techniques in the hazard and risk assessment of aquatic ecosystems, thereby improving the accuracy and relevance of the decision-making process. This objective was addressed by keynote presentations outlining the state of the science and providing case studies, followed by work-group discussions focusing on 4 main areas: 1) Improving stressor-effect diagnostic capability in the assessment process; 2) maximizing efficiency, quality assurance and quality control, and broad-scale applicability of in situ field bioassays and experimental approaches; 3) determining the ecological relevance and consequences of individual and food chain-based effect measures; and 4) incorporating results from field-based effect methods into a weight-of-evidence decision-making process. Major outcomes from group discussions are highlighted, and future priorities for research in this area are recommended.