Life history information of macroinvertebrates is an important variable to consider when interpreting the results of toxicity tests. The importance of life history information has been recognized in the culturing of macroinvertebrates, but only in the last 5 yr has emphasis been placed on using this information in the design of acute and chronic toxicity tests. Sensitivity of organisms to toxicants is affected by nutrition, physiological requirements, behavior, predator–prey interactions, substrate, current, and light. There is need to integrate these, and other variables, to produce more defensible tests. Some features of life history may be used as end points in tests. Key words: macroinvertebrates, life history, toxicity, tests, design, sensitivity