Satisfactory laboratory performance is critical to the use of aquatic toxicity tests in regulatory, industrial and research applications. Quality Assurance and Quality Control (QA/QC) practices are fundamental to demonstrating satisfactory performance. Laboratory aquatic toxicity test procedural and performance criteria can help a potential client decide that an aquatic toxicity laboratory will meet a need, as well as help an outside reviewer determine that test results are valid. Laboratory practices to assure and control quality include training staff, using standard procedures, and keeping valid records, but also include evaluating and improving performance. These components echo several widely used quality management principles. The costs of poor quality (lost time, lost production and lost image) touch both the laboratory and the laboratory's customers. While the level of quality should reflect the use of the study, higher quality work provides for better control, better data and better service, benefits ultimately shared by both the suppliers and users of aquatic toxicity data.